I have both and the 45c is a bit bulkier, but not so much that it makes all that much difference. Note that the barrel on the 40c is 3.5" and the 45c is 4", and a full mag of 45s are heavier.
I use a Galco King Tuk IWB and as long as I'm wearing more than shorts and a tee shirt, its good to go. But that's true of either.