I also did Multi/IR before the CPL, mainly to reduce the instructional hours required for the CPL. My route took me 15 hours IR of which 5 could be in the ground based sim with the multi thrown in with the 10 hours IR!!!!! That was a baptism by fire after not having flown fixed wing for 16 years or so :-) After the M/IR I found the CPL a touch boring, especially having to get into a 'non complex' warrior before being allowed to fly the 'complex' arrow
The plain answer is, if you don't want to 'waste time' then go for the IR and then the CPL. You won't regret it, it will enhance your skills for the CPL no end.
Good luck.
(Just wanted to add that I had a heavy helo Multi/IR before starting the training, hence the CAA dispensation for fixed wing training, just before the LASORS guru's start shouting :-) )