Entry-mid level triathlon/TT bike?

FIT, FIT, FIT,

If you've had a professional fit, they should give you what would be your "nominal" ideal fit for a TT bike.  That, more than brand, age, or components will set you up well.  You can generally find geometry details even for older bikes online.  

Shimano 105 are mid-range (Dura-Ace, Ultegra, 105, Tiagra, Sora) were the Shimano lineup best-to-cheapest a few years ago.  Some on BT have run Sora drivetrains for several thousand miles per year.  Is it worth an extra $200 for Ultegra over 105 or Dura-Ace over Ultegra?  Some think so, others don't (capitalism at it's best!!!)  

If you're looking locally, see if you can get a candidate bike thoroughly inspected before you buy (especially Carbon Fiber).  

If you are looking for another SC in a Large frome I can probably make you a deal you can't refuse.

Yep, too big.

but...but...it's too good a deal to pass up!!!

I wouldn't fixate on the year.  A older bike in excellent condition beats a newer bike that has been hammered and abused any day. 

After you know what fits, pay attention to condition and the bike's history of use and care, and since you have budgetary concerns, also pay attention to things like whether you will need to replace some components right away (cables, chain, cassette -- they add up quickly), and the condition of the wheels.

In general, all other things being equal (but they never are), the faster and harder you will be riding, the more a higher end bike will make a difference.  (Warning -- the difference the bike makes pales in comparison to the difference you fitness and ability make.)

(I'm talking about percentage of finish time, not absolute time, of course.  In terms of absolute time, it takes much less savings 'per mile' to add up in a 5-7 hour IM bike ride as opposed to less than an hour in a sprint.)

In the category of "For What It's Worth" (probably not much):  You'll see plenty of road bikes in an IM, and some of those riders will ride to some pretty decent splits.  At least in the sprints and Olympic races (non-drafting) in my parts, nobody on a road bike is even near the front of the pack on the bike.  That's probably because you really are doing a more or less all-out time trial at those shorter distances, and for a race of that nature, a bike designed for the task makes more difference.

Yeah, that's why I would suck at selling cars.

I'll make someone a hell of a deal on a really nice bike.....but I'm not gonna sell it to someone who may not know it's not the right bike for them just to get rid of it. 

Besides.....it's hanging on my weight rack....and if I sell it I woun't have an excuse for not using the weight rack......and I DO NOT want to start using that.  LOL