Mercedes Chad,
If you get the 170" wheelbase, extended, (170 E in your terminology) it makes no difference in towing capacity.
All the "E" (for extended rear) Sprinter vans are 5,000 lb. max. towing weight with a 500 lb. limit on the tongue
weight.
The 3500 (516/519 series) with Dual Rear Wheels (DRW) will prove to be a far more stable towing platform.
If I were going to tow close to the 5,000 lb. towing weight limit, as you are asking about, I would opt for the higher
rated 170" high top/short back (I.E. NOT the extended rear).
It works extremely well and the towing capacity is 50% greater @ 7,500 lb./750 lbs. tongue weight.
The extra length is nice, but it diminishes the structural integrity of the rear section of the Sprinter body,
Roger