So Ive been playing around with it a bit. Basically the one 12.5KW inverter is the way to go. Thats a 1.2 DC/AC ratio. I am looking at a min $450 premium to go past the 12.5K unit (12.5 K is $2650, 15K is $3107, a 7.6 and 6 would be $3160). Depending a little on what I put in for albedo, I am looking at about 1% loss from clipping with the 12.5. The system will make 21 MWH/yr (everything was with 64 panels) so I will lose 210 KWH/yr. So 15 year payback. Oh, none of those figures include shading, havent gotten to that yet. There will be a little in the morning and evening, but nothing major. So thus I havent been able to assess the gain from more mppt's. Still, I doubt it will make a significant difference. Plus, I have 68 panels already, so they are kinda "free" which makes it tough to justify spending real dollars to trim some clipping losses when I could just add a few more panels.