Well, after much thought and trial, I went with a set of MP-57, DG R300, all set 1 deg flat, which have now been in play for about 1 month.
Overall, a good change - the feeling seems to be better than my MP30's, which means I'm probably hitting more shots out of the middle of the club and I've also gained another half club in distance, which is a bonus.
At some stage in the future, when I am really comfortable with the clubs, I may book myself in for a Mizuno fitting session to ensure that there are no other performance gains to be got.
In the meantime, thank you Mizuno, great clubs.