Comparing wine to a full system emulator is your first mistake. It's more akin to running things in a chroot then an emulator. Performance wise it's great as long as the program you are using works perfectly.
I'm a super admin very a couple of dozen games on the appdb with ratings between garbage and platinum and the truth is that nowadays I'm disappointed where wine doesn't run something out the box. It's older games that it struggles with, for instance RAGE worked out the box for me yet something like Starfleet Command 3 doesn't work at all.
If it works, wine is as quick as running something natively. I've never played Eve online on windows for instance, I have no need to. I wouldn't do anything mission critical with it though, don't let the stable tag fool you.
-Maq