inner barrel questions

So, I have a Bar 10 which I'm getting ready for a big game. I sat down at the computer and search for tight bore barrels... 6.05, 6.04, 6.03, 6.02, 6.01, even a 6.00 Inner diameter barrel! Which is the best Inner diameter for a barrel on a gun that shoots about 450-500 fps? and has any one used the Tanio Koba rifled barrel? I want accuracy and range. Thanks for any help.

Col. Zombie