A 40' header on a 2588 in 70 bushel wheat and I think you would be crawling along especially if the straw is tough, and thats alot of material going up a small feeder house (compared to the larger machines that run 40's). The weight of the header on that machine would concern me as much as anything. If your fields are flat and the crop is very dry then its probably ok, but having run drapers on various machines I feel a 35' would be a very nice fit for that machine, a 40' and I don't think you would be happy with some of the issuses you may run into. my 2 cents.......