I live in the SF area as well and I chose the R600 (basically the the 105 group of the Shimano compact cranks). I did so for three reasons... one, I have external BB's so I wouldn't have to change them out to something else. Two, I got it for $130 on craigslist, brand new. And three, I've just seen so many bad reviews on the FSA's by people that have installed it themsleves or by a shop. It seems the bolts on the arms can back out unless you use loctite to keep them in place.
I called Shimano and they basically said the difference in weight comes from the chain rings as the crank arms are both Hollowtech 2. I didn't get the weights though.
I haven't gotten to ride it on the road yet, just the trainer, but after dialing in the RD and FD everything shifts smooth like everyone said it would.
If I didn't find it on craiglist I would have gotten the R700 new on Probikekit.com for about $192 as it comes with an Ultegra BB and free shipping and no tax! (look under chainrings)
I vote for Shimano. It's a name you can trust and I haven't read anything bad on the Shimano compact cranks.
Good luck!