I also have a unimat 17 with the same problems. A good all-around machine would be one with outboard bearings, larger spindle diameter and enough rpm to get you 60 fpm and still keep a good quality finish. These were not all run at high speed but the versatility is a major advantage. The concept of running a jointed machine is simple. The abiltiy to productively run high speed requires a top notch operator and extremely accurate tooling.
Conventional runs are a lot more forgiving.
I agree with all the other statements on run lengths. I have made the break at 10,000' before I will consider a high speed run. The problem with a high speed run is competition. Large runs are normally high competition and low profit margin. It's not a jointed machine but it does have higher rpm spindle rates which could give you a high quality finish at a good feed rate.