I'm not sure off the top of my head how tall 285's are - there are charts and calculators all over the web if you want exact numbers - but with everything else equal (i.e. if you keep your tires stock) and only swap out the gears, as the number goes up power increases and fuel economy decreases (and vice versa as the numbers go down). So dropping 456's in a stock VX with stock tires will give better acceleration in the low end (city driving), but slightly worse fuel economy on the high end (highway driving).

Accordingly to the calculator at www.4lo.com, and using 29" as the stock tire height, I get these numbers for maintaining a stock ratio:

Tire Height Gear Ratio
29" 4.30
30" 4.45
31" 4.60
32" 4.74
33" 4.89

So the 4.56 would be great for 30" or 31" tires, and the 4.77 would be best suited for 32" tires.

I believe off roaders prefer the really big numbers (like 5.38's?) because you can creep over the rocks really slowly while maintaining power, but SPAZZ can probably better explain that one.