Sounds like you're right on the bleeding edge of being underspined.
Weight of 3 fletch Blazers is roughly 18gr whereas the 4 fletch Max Stealths is nearly 37gr. You're doubling the weight on the rear of your arrow. Without adding weight to the front, you're also losing a lot of FOC if that is...
Easy way to tell if you're going to need to retune is:
1) Check initial tune by shooting through paper
2) Crank up the draw weight
3) Shoot through paper again to see if your paper tear has changed
If it has changed, you'll need to retune. You'll also need to go with a stiffer spine arrow.
For low light, the Sony's are best. A7s is geared toward video. A7r is more geared to photography. Both take excellent pictures. Canon 70d is still a great go-to for all around photography and video. But, the Sony's really shine in low light situations.