If the budget allows look into the KingAir B200GT. B200 with different/new engine and is supposed to true around 300 kts.

I currently operate a 350 and do 295-300 kts. I'm sure you have also heard that the 350 can be loaded up and still do this. Dont think this is so with the others. Guess it will depend on how many and how far you anticipate on avarage.

FBP