Optimizing Number & Size of SSDs w/ SandyBridge ?

Used to be that w/ HDDs & older CPUs, that it was recommended to segregate your OS, programs, data (& even scratch drives) to maximize the storage drive through-puts. Not quite like RAID, but as I understand it you wanted to avoid multiple simultaneous or near simultaneous read/write requests on the same drive controller/HDD. Anything that was faster than the computer's ability to read or write would in essence cause a que.

Now with the memory controllers moved onto the newer chips (Sandy Bridge/Ivy Bridge) and the much higher speed of an SSD, does it still make sense to segregate data read/write requests?

So the question specifically for me is, is it better to have one larger SDD or two smaller SSDs?

Specifically, I was thinking of two 128GB SSDs; one for OS & Programs & a second for temporary scratch/intermediate processing/result data (more important in video editing I think). Now, generally speaking smaller 128GB SSDs are slower than say a larger 256GB SSD. If "request segregation" doesn't matter, then it would seem to be better to just get the larger SSD and do it all on one drive (even if partitioned).

Does anyone have any experience or knowledgeable insight into this?

BTW, in both cases, larger traditional HDDs are planned for Data & Backup.

Thanks.