What's best for your situation is dependent on so many different things and as much as I hate guitar center too, actually testing something out is the best way to get a sense of it. If you can go and listen to it on as close of a system to what you're actually using as possible, that will give you a good idea about how it sounds (e.g. if you track a lot through headphones, bring them with you).
I find it somewhat helpful to look at frequency plots for mics-- they are often doctored, but looking at whatever's published for your C-1 versus what is published for other mics you're looking at should give you a decent idea of how they will at least compare.
If you're going to spend $600, you'll probably get a significant upgrade over what you're using. If you do due dilligence/research you should avoid getting something absolutely awful. I'd check published reviews (take them with a grain of salt-- especially if you see the mic being reviewed on a full page advertisement in the same mag!) and message board comments.
Also, having gone from relatively budget-level mics and pres (Rode NT1000 through ART TPS, or Behri's) to decent intermediate mics and pres (Blue Blueberry, Karma mics through Universal Audio, Chameleon Labs 7602, Safe Sound P1 and Onyx Pres) over the last year, don't leave the pre out of the equation.
