I have had trouble converting to P7, specifically regarding DAZ Figures, got a refund, and then something...; and now just have P6 and P7 installed.  The P7 Figures are new; and I could just use each Runtime as an External Runtime, on the ohter Installation.  And there have been issues like this, with past versions of Poser, that needed SRs to fix; so maybe having our fingers crossed that each version does indeed instal seperately is a good idea?