It can be done with a banshee for sure, there is nothing wrong with your setup, I did hare scrambles for 2 years on a shee, I am not sure how long your races are but here in South Africa the length of such a race is between 150 - 400km long, so first of you need to be extremely fit, the banshee will take alot out of you because of its suspension, so you need a good suspension, some aftermarket shocks, A-Arms, swingarm, axle, and a good steering stabilizer and don't forget a long range fuel tank. And I also found that a twist throttle is much more relaxing than a thumb throttle as well.
And very important, attach some tyre weld on your shee for punctures, and try to take a hydrapack with lots of water as you will dehydrate during the race.
Good luck!