Wish I could experience and troubleshoot these issues for myself, but like I've posted on NVidia forums, I can only troubleshoot what I can't reproduce so much.
I had very few issues on this game, other than low FPS because of the card itself, when I was running it on an HD 7970, and that was fixed almost completely by running on Medium/High mixed settings. Once I got the R9 290Xs and started running in Crossfire, I really didn't have that many issues at all. The few I did were lessed by the 14.6 Betas, and the patch basically fixed the largest issue I still had, which was the stuttering that happened randomly when driving.
The only issue I still have with Watch_Dogs is, after prolonged play (longer than an hour most of the time) when the game's system RAM usage gets up near 8GB, it starts to stutter, very occasionally, not consistently. Exiting & reloading the game fixes it.
Things I (and at least 2 other people I know, one of whom is running GTX 780 Ti's in SLi, the other is running lesser AMD-side cards) don't experience that I've seen droves of others complain about:
1. Stuttering while driving. IF it happens to me at all, it's once in a blue moon, or a product of the issue I just listed where a reload of the game fixes it.
2. Scaling or stuttering issues in general on dual-GPU solutions I have not experienced at all, at any point during my testing. Even TriFire runs the game without issues that could be pointed at multi-GPU solutions, the issue with TriFire was visual glitches, which I didn't figure out how to solve before I got rid of what was my 3rd card at the time of testing last.
3. My vRAM usage does change with settings, significantly, so that's another thing I don't see (vRAM usage being the same at any settings)
It's frustrating for me cuz I like helpin' people solve issues with games like these, but I can only do so much in the way of troubleshooting when I don't have the same issues myself. The guy with the 780 Ti's that isn't having issues says the exact same thing, and he's more direct in saying he thinks people have system issues they need to resolve and that it's not JUST the game at fault.
I think it's a combination of further driver optimization AND a LOT more game-engine work being needed, as the issues should not be being had by THIS wide of a group of their users, that points clearly to it being the game taking issue with things randomly & with a wide-gauge when it comes to who it's effecting.
I also didn't have the issue of not being able to launch it with a dual graphics solution :-P Didn't even know that issue existed, but I wasn't really troubleshooting the game at that point. I only came on forums to start checking things out when I noticed what issues I had before updating to the 14.6 Betas.
P.S. sorry for wall of text lol
CPU: i7 3930k @ 4.6GHz 1.29V (Corsair H110-cooled) ~ Motherboard: Asus RoG Rampage IV Extreme
RAM: G.Skill Sniper Gaming Series (4x4GB 2133MHz, CL9) ~ PSU: Corsair AX 1200W ~ Case: Enermax Fulmo GT
GPUs: 3x HIS R9 290X Reference (Core) Editions in TriFire, Max Load Temps: 71C/70C/71C during OC testing :-P