Note that the exposure compensation trick does NOT work on all bodies--I know on the XD's you're mechanically locked out of combinations of ISO+EC that would exceed that max ISO setting.
Re: what speed to shoot it at--that depends on your subject and your needs. The further you push, the more shadow detail blocks up and the more grain you get. If you're shooting murky night scenes, blocked shadows look completely natural; if you're just trying for a high shutter speed/big DOF on an overcast day, blocked shadows generally look stupid.
I personally prefer TMY up to 1600, TMZ/D3200 only at 3200 and beyond. But it's all about that blocked shadows vs. grain tradeoff. For different subject matter I'd view the trade differently.
Also, you do need to make sure you actually have enough speed to do what you want. If the choice is "sharp but really blocked and grainy at 6400" vs. "blurry but with nice grain and shadows at 1600" the choice seems obvious.