.I have a 5 acres of property in Rising Sun to cut,it takes me and my wife about 2 hrs to cut
I would say it is time for a 24G and a 72" deck. So far I have been able to cut in 3rd gear with my 72" deck and get a very good cut quality. The reason it cuts fast is for a few interrelated reasons
1 - The 18 hp tractor 50" deck combo can choke on high grass in 3rd gear and can leave a poor quality of cut. The 50" deck just can't clear the cut grass out. The 72" really blows it out due to the increased blade tip speed (17,000 SFPM vs 15,000 SFPM) and the deck design.
2 - The added power of the 24G can handle a wider deck. That extra 12"-22" does make a difference.
3 - The higher blade tip speed means a higher ground speed to maintain the same number of cuts per foot.
I have a modified 50" deck that spins the blades at 20,000 SFPM. I have yet to try it out on dense heavy grass. For normal grass cutting, it really does a nice job. Just spinning that deck does suck up 12 hp. I can't use it on the 5665. The Pro-16 handles it with ease.
That 60" deck should perform but I have no idea how well since I don't have one...yet.