The seat is essentially the same with a few minor differences. AVOD is the same. 76Q is obviously a wide body and would actually be my preference with 24 (soon to be 30) F seats. 75X has 26, but also has a 2L door from which to board. The 75X seat is slightly wider (about an inch, maybe sligtly more if I remember correctly. However, the 76Q has 40" pitch where as the 75X only has 37"-38". However, the overhead bins on the 75X are much more accomidating where all of them can fit rollaboards as opposed to on the 76Q where the middle bins have trouble with larger roll aboards.

Bottom line: I would go with the 76Q.