I cooked some more deep dish the other night, one in a lodge cast iron, the other in an old non-non-stick pie dish. 450 degrees for 30 minutes and both turned out very well, and pretty much the same, at least in appearance. We only ate the larger one from the cast iron, which was tasty. My sister just had a baby this week so I froze the second and will give it to her (since my own wife is due next week perhaps she'll just give the frozen pie right back!)
So, for me, the cast iron seems to work just fine. No better, no worse than pie plate provided it doesn't cook for too long.