Jon Austin , Mar 15, 2007; 11:32 a.m.
If the 85's too long, the 100 macro certainly will be, as well.
I bought the 100 macro 4 years ago as a dual purpose macro / portrait lens, and found it too long for portrait (on my then 10D), and returned it to buy the 50mm compact macro.
The 50 is my only non-USM lens, and as such it's a little buzzy when it focuses, but I still love it. It's marginally faster than the 100 (f/2.5 vs. f/2.8), but not so much that you'd really notice the difference in most situations.
Anyway, it's sharp and clear and contrasty and fast and small and light and cheap. I'm really happy with this purchase.
On the other hand, have you considered the 24-70? It's big and heavy and expensive, but it's f/2.8, and would give you more flexibility while your "studio" is still your clients' homes.