If you're boss is even entertaining those sort of numbers and has a discerning taste for speed and comfort then I'd suggest that you get your boss a demo ride of some sort on a Kingair. Faster, more comfortable and much nicer to fly than anything else mentioned and pressurised to get above the weather
PA42-1000, after that you need jets to get better performance.
Navajo with panther conversion on it? 200kt true (iirc) spend a bit of cash on the interior and there ya go. Saw one awhile back with the panther kit on it, leather interior and headrest mounted screens to IFE.
Only need the intake/intercooler modifications, the winglet and four blade props are a waste of time.