The HF tow bar doesn't start coming apart at 5,001lbs. IIRC, the M1009 weights 5200lbs. I've used mine to move my 6,900lb F-350 around in the backyard (which is dirt and gravel BTW) before.
I'd be more concerned with stopping a 5,000 (or 5,200) load with only the towing vehicle's brakes.