Not at all surprising considering that drag increases as a square of speed, and parasitic or form drag of course being the major contributant to overall drag at higher speeds.

What did the finished project end up weighing Mike, dry AND wet? With the FS-70 and pneumatics on board plus the larger fuel tank she must be a heavyweight by now, particularly at take-off?

Where's the ZFW CofG now with all that weight up front? (ie: FS-70, retract mount and visible reinforcing) and what's the forward shift wet with that larger tank? Any tail-weight?

Curiosity begs the question, for as generous as the PC-9 wing is in aerofoil and area, the stock Seagull PC-9 fitted with a .typical silenced 46 two stroke sits at approximately the acceptable limit (2.7kg+/-½kg per unit) for a decent wing loading and power to weight ratio for solid aerobatic performance.