Ah... its better for some things but not all. Its takes higher level, but it won't give you some of the tape compression characterisitcs as easily. GP9 also won't print through as easily. You have to re-bias your heads if you have been using 456. Ive never used 499 so I can't comment on it.
It depneds on what your looking for I guess. Try it, if you don't like it go back to 456.
I run GP-9 and love it, the levels are great, but you're right you do have to push it more to get any nice tape compression....if I remember correctly, I think it's the same bias as 499(?) but it's alot thinner....