The BK117 would be a step backwards performance-wise and tail rotor-wise. Working Cat A from a city rooftop needs the best you can get. Maybe the 145 is 'it' but I can't say without taking a close look at the Flight Manual.
G.
Performance wise BK117 with upgraded -850 engines, (EASA approved STC) has excellent Cat A performance. I'm surprised the option has not taken off more in the northern hemisphere...?