Slings are kinda tough, I personally like the Magpul MS2 slings... would rather have the MS3 sling... soon... anyways, I run those on both my AR and 870, I've tried a 2 point on my 870, but I found because where the sling attachment points were, it made things a little awkward to reload with. Also, with the 2 point I had to slacken it quite a bit to shoot comfortably...
If you can find someone with both then it'd be best to try them out yourself...