Paul
I agree with your comment about horsepower and cutting tools, if you look closely at the cutting edge of tipped tools they are very blunt, this isn't an issue with a machine with plenty of power, they just knock the stuff off, as an old work friend (long gone) use to say "if you put a clog nail in it will cut" small home machine just haven't got that power thats why I think you can struggle sometimes with tips, I've got a good cheap supply of tips but in my home shop with its small cheap Chines machinery, I find myself using HSS more and more, with a good sharp HSS tool I find it easier to hit and keep size. With a tip I think what happens is the inherent flex in the machine holds the tool off, you put a bit more cut on and bingo the tool bites you get that cut plus a bit from the previous cut and your undersize, with a good sharp HSS you don't get that effect so much.
Any way thats just my take on it.
Stew