I to had the 500 with the 28"/3 chokes and smooth bore slug barrels.With this one I took turkeys for years with the full choke and both Rem and Win 2 3/4", 1 1/4oz 4 shot reloads.With the 835 I use the Ulti full choke with the same Win load and Rem's hulls reloaded with size 6 shot 2 3/4 shells.I decided to try Win's factory 4 shot 3" turkey shells just to see how much better they might be.They do add a little reach and are the best I've tried but 90% of the time I doubt you'll need it.I haven't yet.
As far as the deer barrel goes I put Bushnell's Trophy RD on.I get great groups with all slugs I've tried including both Forster and sabot shells.Though I can tolerate it I hate hefty recoil so I put the second thickest pad KickEez makes on it.Reduced felt recoil big time.This pad increased length about 1/4" but still fits me well enough.