Not sure about the model information. We did this on a 720 – straight from V5R1 to V5R3. No real problems at all. We ended up with some application issues, but they were specific to our ERP. Otherwise the upgrade was quite smooth. We even did it in house ourselves (this is our development box). For our production boxes we’re doing a RISC to RISC + OS upgrade as we’re changing hardware.
If I think of anything else I’ll let you know.