I actually have both a Talon (non-SL) and an R3. I bought the Talon about 6 years ago and it was a good value and I really liked it a lot. I've put over 16,000 miles on it and it's held up well. I had been riding an aluminum, non-aero frame before that and it was a huge upgrade. It is smoother than aluminum, and I am not a big guy who is going to flex a frame so that doesn't matter to me. About two years ago I decided I wanted to do some serious climbing and so last year I looked around for something lightweight and went with the R3. In most respects, it was again a huge upgrade, the 2.5 lbs of weight made a bigger difference than I would have imagined and the loss of the aero on the flats hasn't been that big a deal. At the same time I went from Ultegra 9 speed to DA 10. It took me some time to adapt to the more compact geometry of the R3 as at first I found it a little squirrely going high speeds downhill. No doubt the R3 is much, much better, but then again it is five years newer and cost about twice as much, so shouldn't it be?
I don't know why Kestrel is taking such abuse here, but in any event, the Talon design is at least 7 years old now and for that reason alone I would tend to go with something more modern. They do have a newer RT800, I believe that's what they call it, which would be more competitive with an S2. As far as Cervelo goes, I think almost everyone would agree that the S2 is the better choice than the R3 unless you are riding over terrible roads or up big mountains, my goal was the latter.
Good luck.