The value of the micro-stutter improvement with the 670 is a personal one. I don't think any of us can honestly give you the answer you want.
As far as 2GB's being enough, it is plenty now, except in 1 case; modding. If you use a lot of game mods, you may have issues with 2GB's. The only other time it ever runs into issues is with extreme resolutions and extreme settings, particularly AA settings, but those settings are not achievable on a single card anyways.
As far as 2GB's being enough, it is plenty now, except in 1 case; modding. If you use a lot of game mods, you may have issues with 2GB's. The only other time it ever runs into issues is with extreme resolutions and extreme settings, particularly AA settings, but those settings are not achievable on a single card anyways.