Hey Damon
Made finely a flight test this weekend with aux bat.
V2 , X5R, 2x 2700 Tunder power, hovering with small manuvers.
Stability- not good , some raising and movement right and left.
Time- 23:30 minutes , in main left 24% in aux 22%.
Generally , like the results , in term of stability - not so.
Looking for your results for the 6600 and 8000, think I term of stability will be better .
Make sure your batteries are on the top of the mounting plate if you are using the Aero3D plate.
I wouldn't advise 8000 for the X5R, simply too heavy. My application for it is on my X3 i1 V1 for LD.