I have used the 853 style sub-cards on my 933's a number of times now and am very happy with them. I ran them in direct comparison with the cards (two rigs running) and each one I prefer the sub-cards a little more, not that there's anything wrong with the card versions. These shows were in 1000-2000 seat theaters and about 15-20 rows back and pretty much dead center.
As far as location, if it's in a spot I was unsure about, like off to the side or at a venue I had never been in, I'd go with cards as they are going to be the safest choice, but the only real way to tell where the sub-cards will/won't work is to actually try them in those locations. Not something you can always do if you need to play it safe to make sure a good recording comes out using the cards, but if you can run 2 rigs or someone is rolling next to you (or elsewhere) it might be worth experimenting with.
As far as crowd noise, I think the sub-cards act more card wise than omni wise with crowd noise, they do allow a little bit more in, but not overwhelming like the omni's can get. But the sub-cards also give a little more of the omni advantage in bass response and fullness than the cards.
Overall though, I think the sub-cards deserve more attention than they get and I will definitely be trying them in more situations.