I am looking into investing in a Canon 400 2.8. I have gone from a Canon 400 5.6 to my current 100-400 II but looking to take the next step and adding the extra needed light for night games. This will be used for shooting sports and wildlife. While I'm aware it is on the shorter end for wildlife my main use is sports so moving up to a 500 f4 is not an option. I already own a 70-200 ii and 24-70 ii so the lower end is covered. My question is in regards to the lens itself. While I wish I could afford a new Canon 400 2.8 IS ii the cost is way above the budget. It looks like my options include 400 2.8 mk I non-is, 400 2.8 mk 1 is, and 400 2.8 ii non is all being bought used. Knowing that my shutter speeds will invariably always be above 1000/sec and either be on a monopod or a tripod am I going to miss having the IS at all? Are any of these three better quality than the other? Having to buy a used copy, I have read that Canon no longer services any of these models would that be a concern for purchase. Any help would be appreciated.