First of all, there have been a couple of false claims made here, but people repeat what they read in other threads (which I'm guilty of myself).

The SRAM Rival and Force FD are NOT the same. It's more than just weight. I used to think they were "the same except for weight," but I recently bought a Force FD to replace my Red RD, and I also compared them both with the Rival FD on my girlfriend's bike. The Force FD has a wider linkage where the cage connects to the body of the FD. It is wider than both the Rival and Red FD. Not only is it wider, but there is also more material on the cage itself right around the linkage. This is surely why the Force FD is known to be the best performing of the three. Also, the finish of the FD cage is polished just like the Ultegra and Dura Ace FDs are. The Rival cage has more of a rough/matte steel finish. The Red is a matte titanium finish, of course.

I have not had consistent and reliable performance with the Red FD on my Red equipped bike. This is why I bought the Force FD, but I haven't had a chance to install the Force FD yet. By the looks of the beefier/stiffer cage design, I can already tell the Force FD will work better. It reminds me of the Ultegra FD I had on my bike before I went to Red. I didn't like the Ultegra group as a whole, but the front shifting was the one thing that stood out with great performance. I hope I get similar performance fromy my Force FD.

As for the Rival vs Force debate, I'd go with Rival and save a few hundred bucks. I've seen/read about more instances of the magnesium Force levers breaking than the aluminum or carbon levers of Rival and Red. I'm also not a fan of the loud white on black graphics of the Force group. Both Rival and Force lack zero-loss on the right shifter, and overall performance will be exactly the same between the two (except for the FD being better w/ Force).

I'd go with a Rival group on eBay for $700 and then switch out the FD for Force. At ~2200 grams it's lighter than Ultegra and almost as light as Dura Ace. I think it performs better than both too. Can't get more bang for your buck than Rival.