If you really want speed try getting multiple fiberoptic lines and a good server. Should set you back about ?1024.99 a month for the next 12 years if you're lucky
Vis = Visibility Ie: What the game renders... goes from back to front, (use r_draworder 1 or gl_wireframe 2 to see the reverse of the normal render)
Blocking vis can have advantages - less wpoly = more room for detail more wpoly= lag +799 wpoly = software can't manage, starts dropping polys = looks crap and lags