Yeah motors kv may be a problem. Mine are only 970 versions.
I'm surprised the thrust didn't go up when you went with the 8x4's.

Found another site with cheap electronics. Obviously it's an engrish one, instead of brushless they list stuff as BLUSHLESS. LOL
http://www.bidproduct.com/part/Produ...S%20ESC_9.html
40 amp esc $25.50
80 amp esc $36.50[X(]
May give a couple a try just for S&G's.