Honeywell has comparative figures for BK117B-2, C-1 and the LTS101-850D mod. The -850D performs much better than all of them. There's a couple now flying in Sydney with the mod and they're happy with it - neither C-1 nor the -850D has an increased MTOW, though; so you still can't carry payload AND fuel...
C-1 OEI is much better than the B-2 (on paper). It's the real AEO figures you need to worry about...