I'll reiterate the stick with what you know. Since you're renting, I'll assume you won't have more than a day or so to play with it first, at best. This is a recipe for bad things to happen, since you aren't all that familiar with the Nikon system. Stick with the Canon.
Definitely agree with what M.ST said, the 5d2 will be cheaper and probably better for a studio situation, and ditch the 24-150. 24-70 would be OK, but depending on the exact shot list you need (headshots, 3/4, body, etc) I'd get primes. 85/100mm, 135mm, and probably 50mm if you need a 3/4. Or go for one of the 70-200, and add the 35 or 50mm primes. The 70-200 will get you the majority of portrait shots, and they are of very high quality. If you really want to open up the lenses and get a shallow DoF, don't forget your ND filters, and make sure they fit all the lenses you will get.
Heck, the 40D can probably give you great shots with any of those listed lenses and studio lighting, although I'd change it to the 35mm, 50/85mm, and possibly 70-200 since the 1.6x crop on the sensor. Good lighting and great glass will give you great photos, almost regardless of what body you are using.