You don't mention how big the part is, or insert grades that you have tried.
Kennametal K090 ceramics (with T-hone) will machine that easily and they will stand up for quite a while under smooth, uninterrupted cut conditions. Much less pricey than CBN, and you can get far more cutting tips for the dollars you spend. I've never been comfortable with running $200 inserts unless the job really requires something special
You might opt for a semi and a final finish tool. This will make the finish tool last longer.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)