This is one case where newer body might be the better choice.
For indoor dance competitions I prefer an F4 or smaller setting for better depth of field, with a higher shutter speed to stop the action.
I think this would be similar to HS basketball in terms of lighting and action.
For that, a cleaner high ISO capable sensor like in the K-x, K-r or K-5 may be the ticket.
You could probably shoot your 55-300 at f5.8 and still use a fast shutter.
This shot is with a K-x at ISO 3200, F4, 1/400. (Lens is Sigma 70-200 2.8 but DOF at 2.8 was too thin for the teams)