My wife is in a swimming competition tomorrow and I was going to use my Canon 70-300 4-5.6 IS. However the IS is on the fritz and flicking all over the place. Am I better off using the Sigma 18-200 3.5-6.3 OS, whose stabilisation is working and just resizing the image? I'll be using a 7D, possibly using a monopod, if the toddler I shall also be carrying doesn't use it as a weapon.