Completely different machines, even with a 'base' (simpler, more straight-forward) 5225. Compared to a 5205, a 5225 is quite a bit bigger, heavier, less nimble, and has many differences, sometimes big, sometimes subtle. Then if you start checking things off on the option sheet on the 25's you start getting into far more complex electronic and electro-hydraulic systems than the simpler 05's have.
Some quick specs:
Wheelbase:
5205 76.8" (MFWD) vs. 5225 @ 85.7" (MFWD)
Overall Length:
5205 @ 128.4" vs. 5225 @ 141.6"
Height (to top of ROPS)
5205 @ 90.4" vs. 5225 @ 101.7"
Weight:
5205 @ 4275lb (MFWD) vs. 5225 @ 4931 lb.
Turning Radius (MFWD, without brakes)
5205 10.9 ft vs. 5225 @ 12.5 ft.
Engines, same displacement but:
5205 - traditional 3-cyl normally aspirated diesel w/wet liners (more readily rebuilt some day) vs. 5225 5-cyl turbo diesel (with no cylinder liners)
Hydraulics:
5205 - 6.5gpm steering + 10.5gpm implement (17.4 total) @ 2755 psi (implement pressure) vs. 5225 5.9gpm steering + 19.4gpm implement (19.4 total) @ 2828 psi implement.
Drawbar vertical load rating:
5205 1225 lb "regular position" vs. 5225 rated at 1675lb fully extended, 2470lb short position
the list goes on but as you'd guess from those numbers just eyeing them up side by side at the dealer would quickly give you a feel for the differences.