The Phenom II has a better chance of not bottlenecking a GTX 670. However, indeed at 1080p, there are some games that indeed will be bottlenecked slightly by a Phenom II @ 4.0GHz, however, these games are few, and still 100% playable. It depends on the game its settings, and resolution. With a GTX 670, you should be 1080p gaming (1920x1080).
BF3 should be okay for the most part, but online play might take a small hit at times, Guild Wars 2 is definitely being bottlenecked by Bulldozers architecture if you're only getting 20-45 FPS, thats pretty bad.
Is it worth ditching an FX-4170 you already have for the Phenom II? My answer is no. My advice is, if you feel you can do better, consider holding off til PileDriver and see what the benchmarks look like for them when they come out (and ignore numb nuts who may show up in your thread saying X, Y, Z about PileDriver, fact is, it isn't out yet, educated guesses about the performance increase they will bring to the table while nice, are still guesses)
If you already have a decent AMD motherboard, PileDriver may give you a more justifiable upgrade, when upgrading, its best to upgrade substantially or not at all.. If you have a crummy mobo, consider switching to an Intel i5 Sandy or Ivy Bridge 2500K or 3570K respectively. i3s will be more or less a sidegrade in most situations despite obviously being superior for Guild Wars 2.