I think ditch the coolant and go with an air blast or even nothing. Facing steel you can get a negative effect from the coolant because it chills the hot insert and can cause micro-cracking leading to edge breakdown.
You should be able to take the speed up to 450, maybe even higher with a good depth and feed like you are considering. When everything is nicely setup the majority of the heat from the cutting will end up in the chips and your inserts and the part should be cool enough to touch even if only briefly. Your chips may even come of glowing dull red which is pretty well the best condition.
Also you will be able to see a characteristic cratering on the inserts a few thou back from the cutting edge. This is where the chip is making contact.
Monitor the surface finish, initially it should have nice clean shiny tool marks but as the inserts start to go it will change to a duller appearance and eventually start showing sort of minute tear marks. This means your inserts should be replaced.
An open mind is a virtue...so long as all the common sense has not leaked out.