i will be puting mods cause i want 27'' at least. even if i have to boar it to a 450 i willI have 27'' Gators on my 450s and although they have the same tread as the mudbug,they are heavier than the bugs. I put 26'' mudbugs on my Brute 650i...I know,stupid, I should have the bigger tires on the bigger bike.
The 27'' did rob power from the 450s but you can always get that back by spending more money on pipes,jets, and filters. For the 400,I wouldn't go bigger than 26''.
589's don't have any sidewall lugs like the bugs and gators.Gators are I believe the lightest mud tire out there.