I didn't think you could get a quality linear polarizer any more, thanks to AF incompatablity. Although the AF of my 300D worked OK when I used my old Cokin Pl with the EF-s 18-55 USM kit lens I had.
Another issue might be adjusting the filter angles with that really deep hood Sigma provide. I guess I will have to go in on Sunday and see what they say. I'll be in Norwich on Sunday anyway, as it's my Vetrens Breakfast Club meeting. A nice fry up, plenty of millitary banter and a trip to the camera shop, a Sunday couldn't really get much better.