Does this make any sense?

I've upgraded from dx to fx, including going from the Nikon D7100 to the D750, freaking awesome camera!

Anyway, the specs said that the 750 had nearly the same
Burst rate as the 7100, about 6.5 fps

Well, I'm getting Way more than that. I put it on continuous high, hold the shutter button and get off a good 12 shots in rapid machine gun succession before the camera slows down.

Same sandisk extreme sd card as well

I put the same sd card in the 7100 and nowhere near as good

So, what's the deal?

No, I'm not complaining, lol just the opposite, but I'm just wondering what else could explain this?

Have you actually timed 12 shots in one second?

At the time that the D750 was made and the manual printed, memory cards were not as fast as those available now, which probably accounts for the increase in frame capture rate that you have experienced. My guess is that the internal buffer in the D7100 is smaller and doesn't allow a faster rate, even with a fast card.

The D750 is not capable of taking 12 shots in one second.
You are either mistaken or you are trolling.

Since it would be very difficult to confuse the 6.5 fps with 12 fps, I think you're trolling for some odd reason.

Lighting is more than just ideal.