Generally the guys and gals that did the IR first at my school struggled to a degree with the CPL. They found it tough to look out the window and all this bashing around in open FIR off airways maintaining your own separation whilst trying to find some little dot of a town with a road going W/E through it and a disused railway track drove them to dispair! Due mainly to the fact that the aircraft had a perfectly serviceable set of IFR kit that they weren't allowed to use until they were off on a diversion leg.
The whole training system is a bit of an ar*e really anyway and we could debate for years about the merits of what we learn in anycase but in my opinion at least by doing the IR last then you can put to bed all the CPL rubbish and be up to speed with things like holds, SIDs, STARs etc which you are likely to get in a sim ride as opposed to debating the merits of obtaining a MATZ penetration which I can guarantee you will not.