You know? You will get canned answers. But I have some experience with these MD arrays.
In my opinion. For your type of load? I swear they run best with as many spindles as you can get in one group, then doll out the multiple LUN's / Datastores you need from there.
Most are going to have you do multiple smaller raid sets, splitting up log and data locations for your SQL / Exchange?
I say no way... We run a similar, maybe a littler meaner load than you, and we ran it on MD3000i's for 5 years. Now I have setup and maintain a couple of MD3220i's for some non-profits. So there is my experience level, if your curious.