Awesome, thanks for that! I don't need a super fast lens. Majority of my panning shots are taken at shutter speeds of 1/100 - 1/160 and I only really shoot on fine days, which means i'm usually shooting around f/8 - f/13 anyway depending on how sunny it is. I use the 55-250 almost exclusively for panning, for everything else I use my 17-50 and my 50 f/1.8.
I've taken some good shots with the 55-250, but I guess what i'm after is something that will provide better color reproduction and better all-round sharpness. I'm not overly convinced on the 55-250mm's IS either, alot of my panning shots are sharp horizontally but blurred vertically. Might be my technique, i'm not sure...
So the non-IS 70-200 f/4L is no good then? The IS version is about $500 over what i'm willing to spend, so I might have to flag that option. The drainpipe would be cool, but they rarely pop up here in NZ. I could buy one through ebay, but by the time you factor in the currency conversion, shipping, paypal fees etc etc, I could've gotten a 70-300L for around the same price.
I've been reading some sweet reviews on the Tamron 70-300 VC. Sounds like it tops the Canon 70-300 non-L, and it's around $150NZD cheaper. It's also around $200 cheaper than a 2nd hand 70-200 f/4L non-IS. Seems to be the way to go I reckon, and unless you want to convince me otherwise, i'll probably pick one up!