Driveshafts
The 8.8 is a fine rear axle, no reason to say it's bad. I have one in the F-150 that I've rebuilt and added a locker, 4.10 gears, and trickflow bearing girdle cover. There are other mods you can make to the 8.8 to make it practically bullet proof. It's a popular axle, mustang guys have them and put a lot of power through them.
Granted, the 9" is nice, but the 8.8 is just different, not better/worse IMO.
Think about it, it may be an option for you to buy a 800-1500 rig that is in decent shape...swap the ZF out of it and put a M5 in it's place...and sell the rig..nobody will know the difference unless they're lookin' for it...my M5 is now in the F-250 and it works just fine, I just loaded it up and brought it to the dump about an hour ago




