how bad the noise/light is and see if the reach is ok. I never considered primes before, but now I see there is a nice price difference. Hmm.. but there is no IS..
and between 70-200mm L mk 1 and mk2, is the $500 difference justified?
RE noise, if you don't already, and you can live with shorter bursts, shoot RAW. Your computer is better at noise reduction that the in-camera JPG conversion. Also, not all RAw converters are created equal. I initially used Canon's DPP, but have switched to DxO Optics Pro mainly for the better NR (1-2 stops higher ISO is tolerable, compared to DPP, with less loss of sharpness due to the NR). Noise Ninja also works well, and I've heard good things about Topaz Denoise.
RE no IS, keep in mind that IS mainly helps correct camera shake. It does nothing for subject motion. So, with a 200mm lens on a 1.6x body, the 1/focal length guideline suggests you'll get a decent keeper rate if your shutter speed is 1/320 s or higher. For most sports, you'll want to be at at least 1/400 s to stop the action, meaning you won't derive much benefit from IS anyway (although it can help steady the viewfinder when you frame a shot with a long lens). Also, bear in mind that for IS to be effective, it needs to operate for ~0.5 s before you take the shot, for full stabilization - and with fast-moving sports, you're often pointing and shooting faster than that (which is one reason the new - and exhorbitantly expensive - MkII superteles have a Mode 3 IS, which is instant-on at the moment of shutter press.
RE the difference between the original and MkII 70-200/2.8 IS - I've never shot with the original, but accoring to many reviews, the original 70-200/2.8 IS was the least sharp of the 70-200 series (f/2.8 and f/4, IS and non IS). The MkII version is clearly the sharpest of the 5 versions. But, it's not like the original could be called soft - but, on an APS-C body at 200mm, the lowly EF-S 55-250mm is sharper than the 70-200mm f/2.8L IS (MkI) with both wide open (but of course, the L lens is two stops faster); at comparable apertures, they're close in sharpness. The MkII, on the other hand, is significantly sharper than the 55-250mm, even at f/2.8.