If it were me, I would wait till the 405 comes out.

I also have the 305, and it works perfectly. I wouldn't ask for anything more ... except perhaps a smaller, sleeker package. Oh wait, that's the 405!

Yeah, the 405 looks awesome. If it works as well as the 305, I'd say it's a no-brainer. Plus, it has wireless docking.

There were two pretty good threads on Slowtwitch about the 405 and a comparison to the 305. I don't remember all the details, but my impression was that there were some feature reductions on the 405 that would give me pause to switching up to it from my 305. Worth it to really look at it, especially if you have and like a 305.

I don't think the 405 was designed with multisport in mind. I believe it is geared towards running. It has the footpod but I don't believe it talks to the cadence sensor. I like using my 305 on the bike and although the 405 is smaller, I don't think I'll upgrade. You've gotta think that's the next logical step though. This stuff is getting smaller and smaller. The 305 is half the size of the 201. Give it another year or so and there will be a 505(?) that does it all.

Ok, maybe I'm just wishing but I'm waiting to see.

Downgrades (if I remember right) include an EVEN LOWER BATTERY TIME (the deal breaker for me) and no alerts (time or distance -- which I really like in an IM as eat/drink reminders).

I'll stick with my 301 until something comes out good enough to get me to switch ;)

Yeah, a shorter battery life wouldn't really allow you to do IM's with the 405. And I guess the transition away from multisport to heavily emphasized run features would be a deal breaker.

I just got trough running the Disney Marathon and at the EXPO Garmin had the 405. Polar still makes better looking watches for daily use in my opinion but I love the features from Garmin. The lady at the booth said that the 405 is still in BETA testing and should only hit the market after March.

Check out the Garmin Edge 705
It's still in pre-production, but GPSmagazine already got its hands on a Garmin Edge 705 and has the first hands-on preview walkthrough available.

Trainer, Navigator, GPS-enabled cycle computer: Garmin's Edge 705 has high ambitions, and promises to deliver heart rate, cadence, turn-by-turn directions, power data, and more. You can even share core data with other Edge 705 buddies after the workout/ride. It's still only a preview, but so far things are looking good for the Edge 705.

As you read through this exclusive hands-on preview, please keep in mind that this is a pre-production unit and some features may be different on the production unit.

Specifications:
Dimensions: 2" x 4.3" x 1" (5.1 x 10.9 x 2.5 cm)
Display: 1.37" x 1.71" (3.48 x 4.36 cm); 2.2" diag (5.6 cm)
Display Resolution: 176 x 220 pixels
Weight: 3.7 oz (104.9 g)
Battery: rechargeable li-polymer, 15 hours life typical
Waterproof: yes (IPX7)
GPS Receiver: High Sensitivity
Maps: Preloaded Basemap, upgradeable via microSD card slot
Lap history: 1000 laps
Waypoints: 100
Routes: 50
Features
Heart Rate Monitor
Bike speed/cadence sensor
Garmin Connect compatible (online community where you analyze, categorize and share data)
Garmin Training Center software compatible
Virtual Partner (train against a digital person)
Courses (compete against previous workouts)
Auto Pause (pauses and resumes timer based on speed)
Auto Lap (automatically starts a new lap)
Auto Scroll (cycles through data pages during workout)
Multi-sport (automatically changes sport mode with a press of a button)
Advanced workouts (create custom, goal oriented workouts)
Quick workouts (input time, distance and pace goals)
Pace alert (triggers alarm if you vary from preset pace)
Time/distance alerts (triggers alarm when you reach goal)
Interval training (set up exercise and rest intervals)
Barometric altimeter
Unit-to-unit transfer (shares data wirelessly with similar units)
Power meter compatible
What's in the Box
The pre-production unit Garmin sent me only included the unit itself and an AC adapter. The full retail version will include the following items in the box:

Edge 705
Depending on the model, one of the following:
Heart rate monitor
Heart rate monitor and speed/cadence sensor
Heart rate monitor, speed/cadence sensor, and data card preloaded with City Navigator for U.S., Canada and Puerto Rico street maps
Bike mounts
AC Charger
USB cable
Owner's manual on disk
Quick reference guide
One Edge, Three Versions

Figure 1: Garmin Edge 705, Front

Garmin's Edge 705 will ship in three different configurations:

Edge 705, Heart Rate (SKU 010-00555-20) - $541
Edge 705, Heart rate & Speed/Cadence (SKU 010-00555-30) - $595
Edge 705, Heart rate, Speed/Cadence & Data card (SKU 010-00555-40) - $710

The overall design of the Edge 705 is similar to previous Edge units, but the screen has been enlarged and is now in color.

The back of the Edge looks to share the same basic mounting system used on previous Edge devices.
Figure 4: A protective rubber flap conceals the USB port
The right ride of the Edge is home to the Menu button, as well as zoom in and out buttons.
The left side of the Edge 705 is home to the Power and mode buttons.

The entire Edge 705 casing is sealed to protect the unit from the elements (the Edge 705 is waterproof rated to IPX-7 standards, meaning it can be completely submerged in water for up to 30 minutes).

The Edge 705 is powered on by pressing and holding the Power button for ~2 seconds. When first powered on, the Edge 705 searches for satellite signal and displays estimated remaining battery life.
The "Where to?" menu shows the follows destination options:

Follow History
Saved Rides
Back to Start
Find Places

The History menu lets you view recent destinations by Day, Week, or Totals.

I'm assuming it has something to do with size and weight.

If it were me, I would get the 305. I don't see any huge advantages to the 405, and I use mine as a bike computer more than a running computer (simply because I bike more than I run) and I like the bigger display that can show distance, speed, HR, and cadence at the same time, in big enough numbers to see.

The only advantage of the 405 over the 305 is the size. Unfortunately everything else is a serious bummer. Well...they do have wireless sync added, but you have to have a USB done, so it's a net-nothing.

I'll use the 405 for training (cause it's smaller), and then the 305 for races (due to multisport mode). Well...we'll see anyway.