I'll second everything Earmonger said. (I run the same setup as him: CA-14 cards > Ugly > M10.) I usually find I end up pushing my gain knob to 8 or 9 without going past -12dB, even at louder shows, but even down around 5 without a preamp it would probably be fine. Hiss doesn't really kick in until the levels are real low.
As for cards vs. omnis, I'm a fan of omni sound as well, but they're less forgiving: You get room echo, chatter from the people behind you, etc. I forget who on here said it (possibly NYCtaper), but omnis are best for situations where the sound is perfect where you're standing; if you want to zero in on the stage and ignore the rest of the room, you'll probably do better with cards.
I'd probably go with cards in both the situations you describe (to filter out the chatter in the first case, and the room echo in the second since you'll be a ways back), but really there's no wrong answer. It's just a matter of which tradeoffs you choose to make, and which annoys you more: thinner sound or muddier sound.