We run 2 32 foot Shelbounes on Deere 9750s.  No, the do not pull hard in fact they pull very easy.  We will see fuel comsumption go down.  The only thing you will load on a combine is the seperating capacity of the machine.  In no-till, residue distribution is vital to sucess.  The one good thing about the Shelbourne is that you don't have to spread what you didn't gather up.  I am aware of a well know custom cutter that ran their 42 foot model and said he didn't like it, but was running 36 foots this year and liked them. However the 32 foot model has been around for some time and is a proven product.  It would depend on your ground and terrain as to what size would work for you.  You can run faster since you don't have to cut it off and generally in 40 to 50 bushel wheat we have no trouble loading the 9750's with the 32 foot Shelbournes.  In lighter wheat it is more of a challenge.  As was mentioned in other posts they are heavier, not unmanageable but heavier.  Hope this helps.