[Dimis]

I'd be happy to be corrected by the experts, but I'd suggest that suspension set up (including: corner weighting, spring rates, dampening, ride height, tires & tire pressures, etc), and and seat time could see you improve seconds, where as swapping your diff ratio probably only tenths of seconds.

Now while you've identified seat time, have you considered what suspension tuning is available to you?

I'd have thought like most racing, it would be about keeping as much rubber on the black stuff as possible at all times. "Staying planted" and thus having the grip available to push for quicker times.

That's my thoery