I fly a corporate C 340. It has the stock 310 hp engines, but has spoilers and VG's. We have set the cabin up for 5 seats as 6 is just to tight, which is fine because or average load is pilot plus 1 or 2 emplyees. It has a nice ride, is a stable instrument platform, and has decent performance. We flight plan 180 knots and 206 lbs/hr.
Because of the small cabin the C340 tends to be more of a nitch airplane, principaly owner flown. If you routinely need to carry more pax than 414A or 421 is a better plane, but the advantage is the C340 go for considerably less money and many are flown by owners who want the best so they often are very well equiped.
Some thoughts
- VG's, spoilers, a good all cylinder engien analyser are IMO must have mods
- Buy a 1976 or latter ( ideally 1978 or later) model (much better pressurization system)
- There is lots of choice right now. My advice buy the very best example you can find, it will be the cheapest way to go in the long run.