I have 350B2 and 407 experience, and have found the 407 to be slightly more powerful and has a slightly faster cruise speed, and a lot faster climb speed.
The split cabin is an issue, but on the plus side, the structure around that 407 rear cabin is tough, unlike the composite (read...plastic) hood covering the Astar cabin. The Astar is truly a crowd pleaser in the ride, noise level and comfort department otherwise.
Don't knock the 407 rear visibility and comfort until you have tried it, the windows are larger than the "L" series, plus the cabin is 7" wider.
I had the opportunity of chartering a VERY rich Austrailian family from a remote heli-Ski lodge to an international airport, they all sat in the rear of the 407 drinking champagne, go figure? Who needs a front seat to view the Canadian Rockies anyway?
As for operational cost, my company deems a 407 is actually cheaper to operate than their previous B2's.