I thought the point of this exercise was optimizationYes in an ideal world. However. The weight difference between the 2 is roughly 4lbs or 2kg. Nothing. That weight difference can easily be distributed though cam band pockets or what ever else the OP is using
All rigs are a compromise ( to some extent) unless its built for one particular type of diving in a particular environment
Seriously, I'd set up for cold water now with a 17l wing and SS plate. Use this for everything, with a plan to eventually get another rig for warm water. FWIW, I prefer SS for warm water since it lets me avoid using a weight belt. I'd only recommend Al if it is the difference between travelling with a carry-on versus a checked bag.