I'm a bassist. The rig I've ordered (carvin bx600) will push 225 watts through the 410/tweeter. Normally, this isn't enough, but the cab has a sensitivity of 107db. Will this cut it, or do I need to add a cab?
Nope, no sig here.
Just depends on how much projection you want. Another cab with only make you sound bigger. I think you'll be fine as long as you arent playing with the master on 10 for multiple hours.
Framus Cobra
Marshall JCM 900
peavey 5150

Mesa 4x12
I'm not worried about killing the cab or amp...the amp is made to go down to(and cool) 2 ohms, and the cab can handle 800 watts. What I'm wondering is if it will be loud enough for decent sized gigs. (like a large church or something)

Another cab would put it at 400w and 15" more air-moving capability
Nope, no sig here.
We don't always play in churches...there was one gig where we played out in the middle of a high school gym with only our amps...that was no fun at all.
Nope, no sig here.