Jeff; It's been proven again and again that smart money buys the best airplane an owner can afford. My guess is that at a minimum, you'll want a WAAS GPS, and ADS-B In and Out. If I had an oil well I would own a Vitatoe P 210. The Vitatoe mod takes a normally aspirated IO 550 (with 8.5:1 compression) and mates it to a turbo charger system that came with the P210. The turbocharger output is limited to 31 inches of manifold pressure, which turns the engine into a turbo normalized IO-550. This is the best of both worlds since normally aspirated big bore Continental engines have the 8.5:1 compression, they are much more efficient than the factory turbocharged TSIO 520 and 550 engines which have a less efficient compression ratio of 7.5:1 and the turbo normalizer provides sea level power out of the engine up into the mid teens in altitude..
It's a terrific airplane. Can climb right up to 23,000 feet without an undue stress on the engine and cruise at over 210 knots. Quiet and in pressurized comfort. Sweet, but alas I don't have an oil well so I can only dream.
S