Tesla coil cap question

im working on the tank capacitor for my spark gap tesla coil. i just had a quick question. i doubt i will find the ideal capacitance i need of 8.6nF. if i cant find the exact, but a close value, would it be better to error on the high side or error on the low side of 8.6nF?

I'd aim for a higher capacitance, but if you can't reach that it's no big deal. You've got plenty of windings on your primary, so tapping to get the correct frequency shouldn't be a problem.