for the normally aspirated, a good tip to look after your endurance is to operate just below where the power jet opens up at around 22.5".
as long as the machine is rigged as per the book and M/R balanced really smooth it will only be around 3 to 4 knots difference between that and max cont (24.7").
but it equates to around five to six litres per hour saving.
if you wish to operate a wet sump engine (VO 435) make sure that you check the surrounds of the idler gear shaft on the accessory gearbox every day for any evidence of oil seepage. That will indicate wear on the shaft or housing and I can virtuially gaurantee that it will fail within 25 hours of first evidence.
failure gaurantees one cough then silence. BTDTx2
it is the reason why there are no more 3B2A's around much anymore they being a turboed wet sump engine.