As for index racing, we tried the 6.50 index a couple of years back after a friend talked us into it.

With a 200 shot the car ran a 6.52 earlier in the night. Figured close enough. This was before the bottle heater so I figured any temp change would be offset by bottle temp/pressure dropping a little. I left late and ran a 6.489. Ugh! Fastest the car had ever been with a 1.37 60 ft. footbraking, LOL! Lots of fun and learned a lot that night about what the car wanted.

We're the first pair in the video.

https://youtu.be/vbXjkCLaNz8

'63 Dodge 330
11.19 @ 121 mph
Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs.
10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft. 3,700 lbs.