We hunt small parcels with .44 magnum carbine ( Ruger M77/44) and Remington 870 12 gauge rifled barrel with cantilever scope mount and Hornady SST sabots. If your 870 trigger is not in the 9-10 lb range, Consider getting a rifled 20 gauge barrel for your 870 with cantilevered mounted scope for better shot placement and use the Hornady 20 gauge reduced recoil SST loads which use a jacketed bullet, offer .45-70 level performance, and perhaps less tendency to ricochet than lead Foster slugs.
Regardless of which cartridge you choose, shot placement is critical for DRT. Heart/lung shots with 12 gauge sabots may not drop a deer in it's tracks and following a blood trail for 150-200 yards after dark and rousting neighbors for permission to recover with vehicle is a PITA. Use something that you can make head, neck or high shoulder shots with.
I've had better luck DRT with the Ruger 77/44.....Scope, crisp rifle trigger....at 20-60 yard ranges with 240 gr Federal factory loads. Pass on 100 yard and longer shots.
I don't have an elevated platform, but agree that shooting down is desirable and would, in most instances, give one greater flexibility in picking safe shots. My limited experience in elevated shooting is that you can get closer shots from up high.
