SB - which LoPresti mods do you have?
IO, Roy LoPresti (of LoPresti Speed Merchants) was Mooney's chief aerodynamicist /designer for a while and the long body Mooney cowls/airframes bear many of his touches.
Little things like having the nav/pos/strobes on the wingtips faired in, tightly gap sealed ailerons/elevators and the laminar flow wing all add a few knots.
My TKS system slows the aircraft down by 5-10 KTS but flying in Northern Europe I wouldn't be without it.
SB