I recently just went through this shopping for mine. The major difference affecting my decision was the 2509 uses all through hole bolts to hold the hub on. The 2511 uses a stud and nut on the top hole, which to me is less reliable IMHO.
@iamdub had a bad experience with this so based off his experience I went with the 2509. Here is a link to his thread about it:
Oh, as for my exhaust plans- I originally wanted the cutout/unmuffled circuit to merge back into the pipe after the muffled circuit and continue over the axle and out the back. Materials and space constraints prevented this, so I just dumped it in front of the axle. Since I now know that the...
www.tahoeyukonforum.com
Another problem I had installing these was mine were not clearanced for the speed sensor and I had to grind notches in the damn things which pssd me off. I have yet to hear anybody else having to do this on their installs.
You also have to cut the ball joint studs down and even then there is barely enough clearance to clear the wheel if you are running 17”. I also just noticed last night during an inspection I have a slight rub mark on of the CV boots from the upper nut.