Hustler Super Z. They'll mow at 15 mph. Get the "springer" front forks for it. I own one to mow 2 acres. My dad owns one to mow more than 5 acres. If mowing in a straight line it'll do 2 acres in around 20 minutes. I have several trees on my lot, a pool and a few other obstacles so it takes me about 35-40 minutes to mow. The things are built like a tank!
Next suggestion would be Dixie Chopper or Exmark. Also, I have a good friend in Mt Pleasant PA that sells mowers. He carries Hustler and Ferris. He might have a good used one that he took on trade. I could give him a call if you'd like. He also might have a 1 year old floor model he'd cut loose for a decent price.
https://frederick.craigslist.org/grd/d/hustler-super-zero-turn-mower/6491224760.html