It seems to me that the results vary by region.
When I installed the NC2 leak from Beans... I went from dropping calls in the same 2-3 places every day to dropping only a few calls a month.
I just updated BajaROM to version 15 yesterday, which includes the NC4 modem, and I've dropped more calls in 24 hours than I did in 2 weeks on NC2. Admittedly, I haven't used it long enough to be sure... but my initial reaction is that NC2 was better.