I'm a little late to this conversation, but I've towed a '98 Outback (about 3500lbs) on a heavy Uhaul car carrier a few times. This was with a '95 SR (3.5DOHC) w/32 inch tires.
It pulled it fine. Power was always good, even if it did need to drop a gear or two. The 3.5 has a high enough redline that it never needed to slow down to that "horribly annoying to everyone else on the road" speed and was generally still passing the big trucks on steeper grades. Fuel mileage went out the window though.
No signs of stress of tranny overheating. Coolant temp was never an issue either. They pull well....likely much better than a F150 or 1500 size truck and closer to a F250/2500.