Thanks to all those who helped me find a digital back!
In the end I changed systems and went to Mamiya and grabbed Brians AFDIII, Aptus 22, lenses etc.
My initial thoughts are just how good the IQ is, it takes my 1Ds3, lifts it, slaps it about a bit, threatens to feed it to the pigs and leaves it as a weeping mess in the corner.
Everything else sucks though, and getting my head around the difference between the two bodies is a harsh thing for me. I don't consider the setup to be bad, more that I've been used to the convenience a 35mm DSLR has afforded me.
What is going to take a while to get used to is the AF points, I get one essentially, ok I can select the sides of the centre but still not fun. Other than the Pentax 645D a centre point seems common in Modular MF systems and I have to wonder why it's still this way. I shoot wide open most of the time so focus is critical and I do headshots mainly and the eyes are my focus point not the nose!
The other, is ISO performance, great up to and including 200, 400 is bad unless you have a fast shutter...but then I'd use a lower ISO - Catch22.
Long term I'm probably going to get a P25+ just for the pixel binning. I can see myself needing to use ISO 400 more often than not.
The lenses, well, online photos don't do them justice, I've the standard 55, 80 and 150. Compact and solid and feel better built than my L glass costing twice as much. It's difficult to guage IQ because the sensor is different but I'm happy with them. I've just bought the 75-150 and once I know what focal length I prefer for headshots I'll either get the 110LS of the 150D. Possibly the 110.
I've a point I would like to raise though. I'm so impressed with the IQ that if it had ISO3200 and dual card slots I would use this for weddings in a heartbeat. I have to wonder why since 2004 the only improvement to this particular sensor has been Phase's addition of pixel binning. I don't need more than 22mp but I need high ISO, we've 80mp backs with ISO3200 so I can't see why we don't have it in the 22 other than for marketing reasons.
I would pay a considerable amount of money to have a MF look to my wedding photos!