can I use longer spring on 04 pds shock?

I'd like to try a progressive rate spring Sunday on my 04 250 sx but the only one I have is a 71-90/260. Can someone explain what this would do when stock length is 250? I can't see where it would make a difference except I guess the preload nut would be turned down less. All I do is off road but I ride at Croom a lot and there a lot of mungus sand whoops. Any help?

Thanks Marcus. I know it probably took a lot of willpower for you not to comment further. fwiw I've had the following pds bikes (along with a yz 250f and an 01 cr 250) in the last 7 years: 98 200mxc,99 125sx,02 125sx conv to 200,02 250sx,03 450sx,04 250sx, all converted for of road in florida ( I still have all of the last 4). The 98 was a horror both ends. the 99 had a great fork (50mm conv wp) and a much better shock.
The 02's and the 03's had to be revalved to go fast offroad. Jeremy did the 02 125 and John Curea did the 03. Both did a great job. Interestingly, for what I do the stock 04 shock works almost as well as the revalved 02 and 03 ones. With a revalve it should work great for my needs. I do agree that for hardcore sx they don't seem to be on a par with the stuff from nippon.