My friend who shoots for GQ and FHM and other magazines uses a 7D and a 24-70mm. I used a 40D last year and got some work published in 944 magazine as well. But, like some of the previous posters have said, lighting is more important for studio work than the camera.
I can post some studio work I've done later and you can judge for yourself if you think the 7D is good enough.
I understood the OP to be asking about upgrading from the 40D to the 7D, which is different than "is the 7D good enough." I knew the issues with the 7D IQ before I bought it and for my non-studio uses it was still a worthwhile purchase, aka "good enough". But IMHO a 40D to 7D "upgrade" for the studio is probably not a good investment unless there are other non IQ features that are needed.