I've also used AT853 cards outdoors plenty, with simple windscreens (the SH-PREM-WS sold by Sound Pros), and never had any problems with wind noise. (See the Breeders show I just posted to DIME, for example.) I'll usually shoulder-mount them under a light shirt, which also helps protect from wind.
Depending on where you're recording from, though, you might want to use omni caps anyway. As you say, one of the main advantages of cards is that they reduce venue reverb — and no walls means no reverb off walls. So as long as you'll be close enough that the PA sound should be louder than crowd chatter, omnis can be a good choice.