@RorrKonn
Sounds like your settings are messed up on both counts.

Blender is silky smooth even on my old system, absolutely no lag at all, even the interface itself is one of the few programs I have that doesn't have an annoying flicker when resizing things - it's all silky smooth here.  Have you made sure the threaded-sculpt option is switched on?

Regards bumpiness, it sounds like you have the curve for the the brush tip set wrong, and bear in mind that the options you see under the Brush section aren't the only Brush options.  Don't forget to expand that area on the bottom left.  I can't compare Blender's sculpting tools to MudBox cause I've never used it, but they're definitley nicer to use than those in ZBrush - so there's definitely something wrong there, somewhere.