Thanks all for your help and advice:
The D16/Viper combo goes and the Mark16/R380 combo stays and gets the US Divers Pivot Matrix from the other rig.
PS this talk of cold water and upgrades, I have used the R380 rig into the low 40s F with good success actually. I can't say I regularly dive at those temps but when I have it has served me well for what that's worth. Not that im not always tempted to upgrade further...
