I wouldn't get too caught up comparing C ratings between companies, as it's mostly a marketing term, and extremely subjective in how it's measured from one company to the next.
All of the packs should suit you quite well. The Kokam cells Orion uses are quite a bit better quality than the others. You will hear a lot of people on here say different, but they really don't know, they're just saying what they use is good. With that said, the voltage will probably be lower than the others (safer chemistry), so if you're racing against people with hot NiMH, you might find the increased voltage is important to you.
I'd say, the most important thing is to first find a pack that fits in your car (w/hard case) and allows you to add enough weight to be legal. That's really the biggest challenge. As for picking one battery or the other, that's a little harder. All the packs you mentioned give you all the great advantages of LiPo, so it's like comparing really great against really really great. Either way, you're going to be fine. Do you know or race with linger there in NorCal? He's probably the best guy to chat with about your decision if you want facts, and not just a bunch of opinions from guys on the Internet that have never tried more than whatever brand of battery they're telling you is the best.