Worth bearing in mind that if you do say 15 hours in a SEP, then 10 in a complex SEP, then the MEP you are flying 3 planes, thus 3 sets of numbers to learn and possibly a little time having to be spent acclimatising. If you're moving straight on to the IR, I think the benefits to the continuity in the MEP will be realised, albeit it will almost certainly cost a few more £££.