Typically a 450 will spin 315-325mm blades, whereas a 500 size will spin 425-450mm blades.
It's not just the extra length of the blades, they have extra width (chord), this produces more lift at a lower headspeed.
A compromise between a 450 and a 500 would be something like the Gaui X3 or a Compass Warp, both of which use 360mm blades and fly so much 'bigger' than a 450. There are some youtube vids of the Warp at very low headspeeds.
The only helis I have now are a MCPX V2 and a MCPX BL, so maybe I'm a bit out of touch.
Cheers,
Graham