occlusion culling problems

hi there , i have got really annoying problem in Occlusion culling , i have created a villa in 3dmax and its imported to unity perfectly , and now i want to use Occlusion culling with it , i created an area and marked every object static ( almost all objects ) some as occludee and some as occluder then adjusted the settings but , i cant lower the view cell size lower than 1 , before unity 3.5 i was able to do that , now after baking it, the result is extremely bad , some objects got rendered even if its behind a wall and some dont render even if i am looking at it with out a wall in between.

also tried using portals but i didnt find the right script to open it or close but also it gave me the same bad results.

also tried using multiple OC areas instead of 1 but the result is much worst.

i tried the 3 types of Baking but so far none made a diff

the speed of baking is much faster than older unity ver but the result is much bad

the poly amount is really high (2+ mil polys in total) so if i didnt use OC , i will not be able to finish the project.

Spec: unity 3.5.1f2 3d max 2011

Pc: Athlon 2 x4 2900mhz (OC to 3277mhz) 4GB ram DDR3 MSI mobo 785-E51 Gigabyte 6850 1GB

Windows Vista x64

hope that there is a way to fix it , cuz i wasted about 1 month trying to fix the problem without even 1% improvement in performance.

thx for adv and sry for the long post.