I've played with the 528 before, but I didn't look at the leg room then. The 500 series has ~6" more leg room than the 400 series, and the 400 series fits me so you should be Jim dandy in the 520.
Obviously the increased power is a good thing on the 500 series vs the 400. For my setup with the larger machines, I am fine with either a 400 or 500 series. I'd want a BMG, bucket, and pallet forks. A bucket grapple could be handy in some I instances, but it would be a requirement for me starting out.