I just went through the same exercise for the last month+ reading, watching videos, and asking questions. I'm on 5 acres with 3/4 acre of lawn and the rest woods, 500-600ft gravel driveway, grading, plowing snow, moving firewood, cleaning up woods, and likely mowing. I initially felt like the B2650 might be too big, then I started to feel like maybe I needed something even bigger since I was doing ground engaging work. But ultimately, I think the B2650 should fit the bill perfectly for my needs. By all accounts, it's a very popular homestead tractor.
I'm a novice in the tractor world, but from all I've been researching, the advice given thus far by others is excellent. You'll want to consider weight when mowing, and filling the tires and keeping the FEL on will increase the chances of rutting out your lawn. So that's why I opted out of filling the tires. I also opted to go with the heaviest 60" box blade Land Pride makes both for it's use and also for ballast those times I need it (using FEL, plowing, etc). This gives me the flexibility to make the tractor lighter for mowing, and heavier for ground work. Once the tires are filled, well...they're staying heavy. From what I've been told, the wide rear tires are less of an issue than the narrower front tires (especially when the FEL is on, that added weight really drives them down).
One other big consideration for me between the BX and B initially was ground clearance. The BX is lower to the ground, and I plan on being in my woods quite a bit with it, so that extra height certainly helps. Not an issue for you if mowing is your primary task.
What other plans do you have for the tractor? Sounds like you're all grass. Maybe a garden? Driveway paved or dirt or gravel? Grading? Plowing? Any backhoe work?
If it's 90% mowing, the cabbed B2650 will be sweet. It may be a little "overkill", but it's the luxury model of tractors in that class. Many on here and other forums have talked about it's finish mowing quality being very good. When going between the 60 and 72, that really comes down to the ground flatness as others have mentioned. The less flat, the greater the chance of scalping the wider you go with the mower.
Another consideration is backhoe. The BX series you have to buy the BX model with the integrated backhoe or choose a model without and add an aftermarket one later. Kubota doesn't have one that can fit onto the other BX models later. The B series however does allow for it. So that too was another aspect that pushed me to the B, since I may want a backhoe in the future and would prefer a genuine Kubota BH if I do.
Good luck with your choice, exciting times! The hardest part for me has been committing to the purchase, it's A LOT of money and you want to be sure it will do what you have planned and even what you have not YET planned. So take the time to think of all the things you are likely to do, and then get the tractor that fits those tasks. Also keep in mind for bigger tasks, you can always rent a bigger machine for a day or two versus spending many thousands more for that bigger machine that you hardly use for those bigger tasks and sacrifice the lightness and agility and whatever other features you'd benefit from using with your primary tasks. Hope that makes sense!
