Originally Posted by
beng1
If you are only going to ride one to three times per week, then you are already going as fast as you are ever going to go, so if you are interested in comfort just go to a bike dealer and say "I want the most comfortable bike you have for $3500.".
Please. Many of us have to work to be able to afford the toys (including bikes) that we want, and many of us have family obligations, as well. Not to mention we don't all live in climates where it's always between 65-80F, sunny, with a light breeze - I, for one, would love to go out right now (short day at work, woot), but it looks like 92F, and I know my body won't be happy with that for more than a few minutes.
I rarely crest 100 mi a week, usually in the 50-70mi range, and I can hold averages in 17-19mph range, so at 16.5mph, the OP can definitely still go faster.
Anyway, aside from the quick win of new, kevlar bead tires, the OP might want to consider a bike fit, as well. It sounds like the OP is new to cycling, and may not have years of saddle time and subtle injuries to place saddle/bar in the right places for speed or comfort, so it could be useful to understand that bit.
Is the OP riding with cycling kit? A non-flappy jersey, and shorts or bibs? How about clipless pedals? Those could also be quick wins.
Once you have those down, I would direct the OP towards new carbon wheels rather than a new groupset - not because new Ultegra isn't great, but wheels are so much easier to install - in fact, the OP could run carbon wheels with Contis and a close ratio cassette when he wants to go fast on pavement, and swap in the OEM wheels, tires, and cassette if he's going on a dirt path, or just taking the bike on a short spin to the coffee shop.
$200 on a fitting (more or less depending on shop and how involved you want it to be). $200 on a set of jersey and bibs. $150 on tires, $1200 for wheels and cassette. Comes out to about half the budget, and the rest can be saved for when bikes with Ultegra Di2 start hitting the market...