Sculpting serious lag

Have you tried different versions of blender?

No! didn’t think about it. I’ll try.

You’re right! blender with 2.70a it work just find. sould I repot a bug?

ZBrush is quite different. It is not based on OGL.
Try sculptris, from pixologic. It is free and uses OGL/GPU.
If sculptris runs OK for you, then we have a blender issue somehow.

Please try the 386 subd cube again, apply and remove the modifier.
Add a multires modifier, jump into sculping mode, subdivide up to level 6 (~1.5M quads) and see if it works perfectly.
Then try another subd level. A ~4-6M is enough for most cases.
On my 5 years old machine, I can sculpt smoothly up to 100M lol, however a ~25M (level 8) is more than enough and I use it for testing only.

Performance on dyntopo is another matter of discussion and already mentioned here.

Please use the latest builds from buildbot.