1D Mk2 or Mk3?
What sort of events? This could play a big hand. If it's mostly good light and uncluttered action, I'd say the Mk IIn will suffice (pass on the II - the LCD is stone age). If you're talking about poor light and more cluttered action (say soccer or (American) football), I found colleagues' Mk III to be more responsive. People don't give enough credit for newer processors making faster acquisitions and putting out cleaner images. If you're making money, even marginally higher percentages of keepers matter.
I find that for many different types of events, I'm trying to get accurate acquisition then typically firing off no more than 5 shots as I anticipate the action. I found many of the criticisms (ie. Galbraith) based on very long stretches of continuous shooting when the camera would lose its way (on bad bodies). That's simply not how I (and many colleagues) shoot. Even if it is, it looks like the problems have largely (arguably of course) been solved. The IIn will never have a faster processor, better ISO, live view, etc. If tweaks are needed (and this goes for any 1D), then consider that a tune-up like you'd do for a fine car - shutter replacements, adjustments, other servicing...get the most camera you can then take necessary care.