As usual in these threads, everybody will suggest their favourite plane
But a 540 doesn't cost much more to run. The extra hourly cost (engine TBO) is 5-10 quid an hour over a 360. And you can do 138kt IAS (about 60% power, say 155KT TAS at 10000ft) on 10.5 US gals/hr. Compare that with the alternatives; well those that you can get reliable fuel flow data. I used to burn that much (in terms of MPG) in an Archer, but a PA28 doesn't even begin to compare with a TB20 in terms of capability, versatility, comfort, access, passenger acceptance, you name it.
Also Socata prices are pretty low right now.
Still, no mention of a budget. If it is 30k and you call popping into cloud "IFR" then a C152 will do the job