I just wanted to finalise this forum thread as I think I can offer some good pointers here for anyone else who has the same dilemma as I did about the PRS Multi-Fit case (confirmed model no ACC-4255).
There were two things that put me off of the Multifit case. First was the fact that its a multi-fit and I thought this would mean the Semi-Hollow was not going to be a great fit (due to the case being designed for several models) and second was the square box design.
The case arrived yesterday and my first concern was actually all in my head. This hard case is a *perfect* fit for the SE SH Custom. Once the guitar is in the case, there is no evidence at all that other guitars fit in here - it may as well be called the SE semi-hollow case instead of multi-fit. You get the idea.
The second concern was somewhat justified - this case *is* a bit of a clunker and would not be fun to carry around for very long. It does have more space for accessories than my other cases, but with only the guitar inside it's 9.5Kg (21lbs) compared to my Les Paul in it's original case at 7.5Kg (16.5lbs) and the Les Paul is a much, much heavier guitar. The LP Case has a leather handle instead of plastic too which is kinder to your hand when lugging it about. For completeness my strat also in an original hard case weighs 6.5Kg (14lbs).
That said the fact that the case is such a good fit means I can kinda look past the extra weight - no way I'll carry it around in there though - the gig bag the guitar came with will come in use for that after all!
Also for the record Sweetwater don't ship PRS outside of US, but I ordered mine from Thomann who handle international orders to a lot of places with no hassles.
http://www.thomann.de/intl/prs_case_vintage.htm
Thanks again for the help along the way.