Al Brown calls it "To chew or not to chew". Meat that you think of as chewy is usually a prime candidate for slow cooking. Shoulder, hocks, shanks, ribs, etc.
Bits that make nice 3 minute a side steaks... the fillets, rumps, backstraps, etc don't take to slow cooking as well.
Chuck steak on the other hand makes for great slow cooking.
I'd just look at the cut diagrams and go from there. Someone else already did the hard work:
Neck and shoulder would be my picks for slow roasted venison.
I'd save your backstrap for tartare or something.