Well Muzzer at least we agree on one thing, The CCGT inserts do produce a super finish and at greatly reduced cutting forces. If they are treated right then they last quite a while even on steel, although I have never tried them on any EN24T yet. I find they handle EN8 well enough. I think you're right about the chipbreaker /seat angle, I must have close to a 100 boxes of inserts of various makes both positive and negative , and there is a plethora of chipbreaker styles. and as far a boring bars are concerned some would be suited better to a specific seat angle. I dont think it makes as much difference on an external toolholder than it does on an internal one.
Jason, I have also got quite a few of what we would deem ME sizes of bars, although I don't make models. I make mostly tooling and any parts for the machines at the employers workshop. I dont think I would have the skill to produce engines such as yours and others on here. I can work to very fine limits if the situation demands it, the modelling side is a different skill set from mine, also I think I would fail dismally on the patience side.
cheers.