Sorry I can't offer you any thoughts on your local track specifically, but the old track I used to ride on here had a front straight of ~2km (1.2mi) & although I never had an XB on it, I did get out on a V-twin powered Honda Hawk I used to own.
The issue I found with torque-focused V-twins on long straights is that taller gearing doesn't always result in a higher top speed because there simply isn't enough top end horsepower to push the bike any faster, especially on a naked bike like your SX. In fact, you may actually find that your top speed, in top gear, drops once you raise your final gearing.
Assuming your local track also has some twisty bits, you may find that you're still better off sticking with the lower stock gearing and just letting the I-4s sail past you on the straights, then reel them back in the corners.
It's worth experimenting with & I look forward to hearing your results!