Bigger creatures more than 5 foot?

[Drakeskull]

Ive been thinking on making it to where a bigger creature can take more that just a 5 foot adjustment and possibly raising there speed a bit. Any views on this. Like a large creature could make a 10 foot step during a full round action. it seems that it would make them more dangerious but more realistic

 

[the Jester]

I did this for a while and went back to the by-the-book method.

Doing this means that pcs of medium or smaller size will never get a full attack against a savy large enemy, among other things. It also means that big bad guys are much more likely to be able to get their full attacks off. Believe me, it doesn't seem too bad at first but after a while you start to realize just why they kept the 5' step a flat 5'.