Those numbers you are quoting are a huge ask for any twin. The only difference would be that with an engine failure in either of the aircraft, twin or single, is the crash site might be in a slightly different place.
The answer to your capacity issues with the same performance would probably be an additional B3!
The B3 can operate Night and IFR, the issue is only the regulations. In light of the fact that you are not going to get a twin to match the B3's performance - change the rules!!
If that is not the answer and it appears you have ended up with either EC145 or AS365, talk to the guys at Nucleo Elicotteri Vigili del Fuoco in Trento Italy. Thay have operated eveything from Llamas to K2's to 117C to B2, now B3 and N3. I think you may end up with a combination of B3's and N3's like they have. Horse's for courses!!
Some of the engine parts are the same at least. Are you operating B3+ (2B1 engine).