Like your choice.
I got an F70 last year. I've managed to rack up 4000km in the last 10 months, and I haven't really had any problems. Just a bent rear derailer hanger due to one too many falls when getting used to the shoes..
When looking at cost, if you don't have shoes, don't forget to factor that in when working out what you can afford. When I bought my bike last year, I added an extra $200 for shoes, pump, bag, levers, spare tubes, etc..
It's worth shopping around, as some places will throw in some of the extras.
If you can hang out a few months, things tend to get cheaper in June (but not always) as the sales start.
I agree with you, I definitely wouldn't go for the F90, with it's Sora shifters.
In other news, I know what you mean about pack riding being daunting in the beginning. When I got my road bike last year, my brother in law was nagging me to join him on beach road (Melbourne's cycling mecca).
I had read about pack riding, the hand signals, the close riding, the snobbism, hey a rider has joined our pack with non matching shoes, time to up the pace, etc....
Anyway, the first time there, I was a little nervous about it. It wasn't long after we started that a pack went by. My brother-in-law nodded, and we hopped on the back. It was a reasonable size, around 15. As we went along, others joined the back, and we swelled to about 30, with us right in the middle. The hand signals were in full swing, and I watched the front of the pack, where some riders were rotating, sharing the load into the wind. I wondered if the rotation would reach back to us, and we would have to do some work at the front.
As I was thinking that, the guy in front of me pulled out, and waved me up.
Wow, first time in a pack, and I'm being waved into the rotation. Maybe they can see potential in me. Nervous, and excited I moved up next to him.
As I caught up, we exchanged hellos. Then he said those words that still ring in my ears today.
"hey mate. Just thought I'd better tell you before others notice, but you've got your helmet on backwards"...
Time stood still....
Thought it might be a good time for a quick stop, and some adjustments.
Anyway, it didn't take long to get the hang of it all. By the time October came, and Around the Bay, pack riding was second nature. There's nothing better than being in a pack that can set up a good rotation where everyone does their bit. The km just disappear...
Good luck with the purchase, and make sure you update us on your progress.