My partner and I own a 1978 J model and in a couple of years (maybe sooner depending on flying times) we will need to overhaul our io360 A3B6D and prop. My question to all out there is : what would performance gains be verses dollars spent for upgrading to a 210 hp io390 non turbo, also with adding a power flow exhaust system (which will be needed at time of overhaul)? We currently have every LoPresti speed mod on the aircraft now and we cruise at 153 kts @ a planned 10gph (exact is 9.7) 50 degrees ROP