Viewport lagg

Hi

Yesterday I’ve tried sculpting in blender for the first time and very soon I noticed that my viewport started lagging at around 4 subdivision levels on a simple uvsphere. I think I’m probably missing some option here because in mudbox I can easily sculpt to 2million poly’s without any lagg.

My system specs are:
AMD Phenom II X6 1055T Processor 2.80 GHz
4GB RAM
Videocard: ATI Radeon HD 5850
On 64 bits Windows 7

Any help would be appreciated.