The last time I looked the RBT was 14. Don't forget maybe 3 to go through your ZF as well.
The gearing available is listed on the RBT page.
You can drop 6th down, go to a 2.50 or 3 something first gear. It depends on what you want to do with the car?
If you want a 10 second car you HAVE to do something with the 2.20 first gear. That really should be second.
Hall put a 5.38 in the GTS and went into the 9's with it. That's the equivalent of a 2.80 first gear.
To me, I just don't see the point in gearing it for over 200. You would need to use that on a Super Speedway
The ass on the RBT hangs out a little more in the rear.
Maybe they will take your ZF in trade towards a 6 speed?
No matter how you look at it, there is more versatility in a 6 speed.