Just to chime in WhiteNoise, the game does appear to have some ATI issues at the time, people are finding it runs quite a bit better on Nvidia cards. Be expecting day one driver or patch. I will chime in and say that my GTX 660ti seems to be running the game nearly perfectly with hybrid High/Ultras, although I did have to force triple buffering to fix some minor stuttering that is likely just from my GPU choking up. Also the game maxed out does look very good, and overall gameplay wise it does definitely give GTA V a good run for it's money, but I won't say it's better, more so a really good alternative.
Also those frame dips you spoke of WhiteNoise seem to be entirely fixed by triple buffering for some reason. Seems to be a common thing with some of Ubisoft's games, cause it helped a lot of people on AC4 with the very same issue.