If you put stainless steel appliances, tiled floors in the bathroom and kitchens, finish the basement, and put granite in the kitchen and are in a half decent neighborhood, your units will rent a lot quicker.

My thought process has always been pay it down fast, to not only avoid interest payments, but also get higher monthly income quicker.

Updating the exterior areas can be done for pretty cheap and increase curb appeal greatly, giving off that fresh new look which can attract tenants quicker and help justify an increase in rent. 

It sounds like the turn around time will be a lot quicker on the single family.Also, how desirable are duplexes in your area?

If I were you, id high ball everything , sounds like major damage to this house     maybe shoot for 60k rehab, high points on the hard money..... even if you buy cash at 30k +60k + hard money fees + closing costs ... you might be able to squeeze a 10 percent return out ..... if you have good contacts id say maybe It could work ... if you have only done this a couple times , maybe pass on this for something with a quicker turnaround time 

Another way that might be quicker...

It will not get me more in rents, but will probably get the house rented quicker imo.  

Concerned stocks could lose more value and quicker than performing rentals3.

If you're anticipating a lot of usage out of your suit, I'd highly recommend getting suit separates with two pairs of the same pants (since the pants get worn out much quicker). 

But just looking for a quicker answer.