Interesting that it bogs down. You need more revs in that case and keep the fine line between bogging down and lighting up the tyres.
In my experience in the 1/4 mile, short shifting does not result in quicker times. Ever. Plenty of people do it and fail miserably to get a quick time.
Try holding the car at spool, let out the clutch reasonably quickly and feather the throttle at 50-75% of max initially in 1st to near the max power point (rather than to max revs) and then changing to second, again feathering if needed until grip occurs. It seems to work in most of the front drive cars i have driven. Then there is the bum/brain dyno part or "feel" which experience with a car helps to understand how best to get the most out of it.
Less weight will definitely make a positive difference to performance. That and throwing the air conditioning in the bin. If you are running 360bhp and doing 13.1 with a full interior, you will make 12.9 with the rear seat, passenger seat and spare wheel etc out the car. Try a light weight battery too - you lose about 15kg with that
Knockhill - thats really where you want to be. That power, a diff, good suspension and decent brakes (make sure you have DOT51 in there) and you will be chasing, scaring and beating a lot of so called faster cars like Focus RS's etc round the track