Dave, can you give some more info? Still not enough to be getting on with. Firstly can you define what you mean by crater wear and an image would be even better. Also the conditions you are cutting in, the job the set up, the material, clamping etc. Again even better a image of the job you are working on, on the machine would help a lot. It can sometimes be a small combination of various things that lead to problems that are hard to define by single bits of info.

I don't see those speed and feeds to be a problem considering the recommended rpm, but it maybe a problem for your machine. Remember the recommended feeds and speeds are like fuel economy figures advertised by car manufactures. Its best case scenario in the best possible conditions that can not be repeated in real life. Your machine designed for ally or not if its still probably a inherently weak gantry style machine by the very nature of gantry style machines you are fighting the odds from the outset but that does not necessarily mean it is the machine. Again its down to cutting conditions. More info will help a lot.