I have the SM7B. In my case it needs about 55dB for screaming, 60dB for melodic singing, and 65dB for quiet parts. Some audio interface preamps go up to 60dB but not cleanly, there's hiss up there.
I guess the number one perk of that mic for me is how natural and true it sounds to my perceived voice. Also how dry it is, meaning it takes reverb all the much better.
You can make it more condenser-like by taking off the wind screen and using a pop filter, and boosting the high highs a little in your EQ. That plus some compression results in a pretty detailed and crisp, but not harsh, sound that is smooth at the same time, even on soft vocals. Only thing I wouldn't recommend it for is airy fairy Mariah Carey type whispering. Also check your distance from the mic. 1 inch has worked well for me; the capsule's further back in there by a few more inches anyway.
If you have good room acoustics and/or treatment, or a nice vocal booth, I think you can get a slight better sound with an LDC since it has more detail and sensitivity and isn't as pre-amp dependent. But the SM7B will give you a drier and more direct 'in your face' sound right off the bat if that's what you're going for.