I still have lots of fun playing against him in legendary difficulty. It really puts your skills to the test, knowing that a single whiff or unsafe move can end up with your char pretty much KO'ed. I also use fights against inferno to check on my actual skills with any char before going online with him/her. If I can consistently beat the whole ladder + him with no retries, then I consider myself ready to try online with that char. Of course this is by no means any kind of formula, but it works for me.