32 bits program will still be limited to 2GO memory, but the good thing is, you will be able to have more of them open simultaneously (I have 8 go on my computer, and being able to have photoshop open with huge files when I tweak my textures in my 3D app - a 64 bits one - is certainly a big advantage (I guess, have poser open too and it would still make no difference, while, on a 32 bits system I would keep swapping to the hard drive)
You shouldn't notice a big increase in speed, the big difference between 32 bits and 64 bits is essentially memory addressing, other than that, don't expect too much difference (some people did notice a slight speed increase, but not enough to be really noticeable - maybe 2 minutes on a 20 minutes render)

J-L