Well my project is complete for the moment, replaced my two 500G HD's with an SSD for system and one 1.5TB for media. For all that expense, what we achieved really was a much cooler case temp, so I could slow the fans - & no HDD noise as the family are still sensitive about watching a "PC"
I used the OCZ 30GB series V2 and aside from a couple of minor issues moving the OS over, it has made the HTPC into a much slicker machine. It's not yards faster in boot or anything and that wasn't the objective, but what we do have now is a piece of equipment that looks & performs like a hifi bit of kit, totally silent boot up and operation. I am really pleased with the outcome, it was the final piece de resistonce.
The only thing I could wish for now would be a less noisey blu-ray/DVD drive, it sounds like a vacum cleaner when it spins up a disc.
For anyone thinking of doing similar, note that we haven't really gained any speed here, just heat and noise reduction.