Don't be scared of turbochargers. I don't know why on earth so many people look down on turbo's.
A turbocharger is hands down the most efficient, reliable, and bulletproof system for forced induction. If you purchase a 3520 or 3720, you will likely never replace the turbo in your life time. These are small engines with low power and heat output, I wouldn't worry one bit.
The 3320 tractor is quite underpowered from what I have heard in the past. I know for myself, I wouldn't even consider purchasing a tractor of any kind without a turbocharger, except for the X748 that I have, which obviously has absolutely no need for it, being a garden tractor and not a utility machine.
If this is the last machine you want to buy for a long time, step up to the 3720. With a hydrostatic drive system, it makes a tractor feel underpowered right out of the gate, versus a geared tractor. The more power you can get, the better the tractor will perform in your tasks.