I honestly would go the exact opposite route.

I would get the "Best Fitting" mediocre frame I could find and equip it with the best parts I could afford. (focusing on drivetrain)
Reasoning?

Point 1
The most aero frame in the world might save an elite rider 3-5mins in an IM effort. I think 3-5 is also VERY generous, as what the wind sees most is....YOU! The rider is, by far, the most un aerodynamic part of a bike. Changing from sitting up straight into the wind vs aero can save you 20+mins on the same IM ride (given equal power output).

Point 2
If you want to get faster at riding, you have to ride more and put out more power. This will put more strain on the drivetrain of the bike and cause parts to wear out more quickly. If you can't put the power down to the road, you can't go anywhere. "It's not the bike. It's the engine!" A good engine will put out enough power to wreck cheap parts bin components.

I would much rather have a great fitting Felt S22 with dura-ace than an ill-fitting DA pro built with sora.

I think if you follow a similar line of logic when picking out a TT bike, you will be well served. You will own a comfortable bike that won't break down on you every season and won't "nickle and dime" you right out of the sport.

It can be so easy to fall into the whole "transition area street cred" mentality. "Oh look at that fully carbon _____ with a Zipp 909 disc, HED 3, carbon water bottle cages, and extremely aero riding position. Because....hell it looks cool. Then, during the race you notice it's riden by a 60+yr AGer that rides at 15mph on the base bars cause the aero position is so extreme it hurts.

weight is irrelevant on a flat road. Most triathlons bike courses are not set up like the swiss alps. Therefore, spending the extra money on an all carbon frame to shave some ounces doesn't make that much sense to me. (unless you have the money). However, AERODYNAMICS plays a huge role with the TT bikes. Therefore you should find the most aero frame you can, even if the frame is alum with carbon fork etc.

You dont want to be cheap on the drivetrain. I would atleast get 105 components. I think the difference between tiagra and 105 is huge. With the extra money you will save on an aluminum frame and 105/ultegra or force/rival components, buy some good race wheels. Most bikes in the 1-2,000 dollar range dont have a great set of race wheels.

best of luck!

trekrider - what do you consider a race wheel?

J.Michael

35MM rim depth is a good start for race wheels IMHO. They dont have to be carbon. And I would still go with clinchers for obvious flat reasons.

thecozz

keep the wheels that come with your bike. Train mostly on them, but run your race wheels to get a feeling for them and feel fast! Most people dont ride their zipp 808 or 404 on a typical group or training ride. Some do if they have the coin!

best of luck!

Definitely go with 105 components.
Race wheels are going to run you $1,000. Definitely nice to have, but not necessary. You can expect to see a speed advantage of 60-90 seconds on a 40K course with better wheels. In terms of time saved per dollar spent, not much of a bargain.
You definitely don't need to spend $2,000 on Zipps. I'm partial to FlashPoint and Williams wheels in terms of bang for the buck, but there are plenty of opinions out there.

The advice I've given folks is to buy your stuff in the following order:
1. Best bike you can afford with at least 105 components. If "best you can afford" means you're gonna drop more than $3,000, then just know that over that price point you're buying for "want" rather than "need".
2. Wesuit, aerohelmet: Cheap ways to get some speed
3. Race wheels, or rent race wheels. Keep the old wheels for training.

For what it's worth, my all in cost for a Kuota K-Factor with a 105/DA mix and FlashPoint FP60 wheels was around $3,000. That was four years ago, and I haven't had to upgrade a thing. The bike's still faster than my engine.