I did my ME and IR first too and already held an IMC. I was attracted to the cost savings, but I think the reduction in minimum hours for the CPL from 25 to 15 is quite generous. I wasn't ready for my CPL test after 15 hours of dual so the additional hours I flew wiped out most of the cost savings.
I thought that having the IMC was helpful as I already knew most of the theory, but it will probably work out more expensive doing an IMC first as it might save you a few hours on the IR but probably not enough to justify the cost of the IMC if you know what I mean.
I was happy with the way I did it though and found my flying became a lot more accurate after the IR which set the scene well for the CPL.
Hufty.