A group would have quite a bit of an aero advantage as well, so even if the guys there were putting the same watts down as you, they would be going faster.
On the bike...IMO, of course...and sorry if I am repeating stuff you already know...
1) Watch the gearing on the road bike. You may have a triple or pretty big rear cassette on the current bike and some road bikes may have 25-28T cassettes and not have compact doubles on the front. As you go further, you are going to find more hills and might want those gears.
2) Watch the tire clearance. You aren't a huge clyde, but if you end up needing stronger wheels and/or bigger tires, they may not fit with your frame. This is probably way less an issue now as disc is more prevalent and the tiny tires are out of vogue, but I bring it up because when I got my Scott CR1, though it was more of an endurance bike, it was based on a previous race frame and tire clearance is really tight. I got the bike because it was carbon, ultegra and a great price and love it, but the tire clearance is troublesome.
3) IMO, the better groupsets are well worth the money, so 105 is the minimum...Ultegra is better if you can swing it.
Good luck with the shopping.
DaveW