Is that at native rez on your 27" iMac?
Yes, native resolution. I also have an external 21" Acer monitor connected as well for dual-screens but when playing GW2 I'm using fullscreen on the iMac monitor.
So here are my fps comparisons (note; I only did this quickly to test and I'm only at level 10 on my toon. I barely engaged any combat and it was more of a general fps test in some areas):
1. Bootcamp Windows 7 64 Ultimate - All settings are maxed in game and I am getting around 50fps in Divinities Reach and around 40fps throughout the Queensdale area.
2. Mac OSX 10.8.1 - All settings are maxed in game and I am getting around 40fps in Divinities Reach and around 30fps throughout the Queensdale area.
3. Mac OSX 10.8.1 running Parallels 7 using the Bootcamp install with Windows 7 64 Ultimate - All settings are maxed in game and I am getting around 35fps in Divinities Reach and around 25fps throughout the Queensdale area.
When comparing the three; running the game in bootcamp feels slightly better or more smooth. But nothing that makes me want to boot into windows. As a matter of fact I will probably jump into this game a lot more now that I don't have to boot over.
Everything felt fine with the Mac version. I have not run into any issues, just a bit of a loss in fps.
As you can see running in parallels wasn't much lower in fps than on the Mac. However, running in parallels definitely doesn't feel smooth. Lots of hiccups in parallels and little things like losing control of your "view" when moving around randomly. This doesn't happen in bootcamp or on the OSX version. That's why I would only randomly use it via parallels to do a few quests here and there (just to avoid rebooting into windows).
I'm happy with this port and excited to play the game more often as I can avoid the reboot.
I'll test my i3 iMac when I get a chance and post back here.