I have a
B2910, but I have never looked at a
B7800, so I can't give you an objective comment, just my experiences. The seat on the 2910 is pretty comfortable, and the armrests are very useful in most situations, and they rotate up out of the way when you need more room, like when you are turned around in the seat watching what is happening behind you. Or you need to look over the edge of the tractor to see exactly where the rear wheels are. BUT, since the tractor has no suspension, you will feel every bump travel up your spine, so the seat is the only insulator from ground shock. The 2910 seat has adjustable springs under the seat so you can adjust it to your weight, and that makes a big difference. I also have a lot of back problems and I can work for several hours before I have to rest my back. I'm sure that with a standard seat, I would be forced to take breaks much more often.
As far as the cruise control, I absolutely love it, and I would never have another tractor without this same design. You can adjust the speed without ever having to move your foot, from a slow crawl to full speed. But the cruise only works in forward, you have to use the heel pedal to reverse direction. Now, I mainly use the cruise when I mow 6 acres of grass, but I have used it when I built my road, tilled my 6 acres for grass seed, moved dirt, logs, brush, and anything that I will be going at a constant speed for more than a few minutes.
One other thing the 2910 has that has really been beneficial are the extendable rear 3PH arms. They make hooking up your implements a lot easier on your back if you don't have the implement on dollies. I don't know if the 7800 has that feature or not. By the way, you will be able to store and hook up your implements a lot easier and faster if you make dollies for all of them. Struggling with heavy things like tillers, box blades, or any implement that weighs over 200 pounds is very hard on the back, without the ability to roll them around on wheels (if you have a hard surface like concrete floors). If you have any specific questions about the
B2910 or
B7800, you will find many happy owners of both, willing to share their opinions.
Good luck with your purchase, they are both good tractors, as are most all of the compact utility tractors.