Sorry I'm mixing them up I meant the rhomboid CNMG not the triangle.
Note the second letter, this indicates no relief angle, usually reserved for double sided inserts. Because there is no relief angle you need the tool bang on centre. You might get away with a touch low, but certainly not high, even a nats wotsit too high and you'll be in trouble.
Yeah, I think I am (or, rather, was) running it a gnat's high. Which, now I've read up on insert codes & rake/relief angles, makes sense. I've been doing that all afternoon instead of working, oops.
I believe they are intended for larger powerful machines with higher removal rates and don't really suit us types.
Try CCMT or CCGT in that order.
As for nose radius I doubt you'd notice the difference .... let us know if you do ....
Wilco, ta. If the difference in nose radius is that small, I've no chance of spotting it

I presume that the tapered hole (the "T" in the code; and I know it's not T for Taper, that's just a happy coincidence) won't be a problem with the mounting scheme I've got? It's got a sort of pin arrangement which pulls the insert back into the holder (tool code is PCLNR 2525M12), the insert that's in it is a straight hole type ("G"), but no-one makes a CCMG or CCGG; or even a CCMM or CCGM, because I assume that with a relief angle the insert gets a distinct "top" & "bottom".
Am I making this too hard for myself? Should I just buy the cheapest CCxx with a hole in?
Carbide don't like sudden heavy loads as you have found out
Even a stall or a belt slip will take the end right off .... it can get expensive if you are a bit clumsy.
If you want to cut something irregular like hex or square, use HSS till it's been made round 
I'd always planned to go HSS pretty well exclusively; but these three holders were sat there... if I was buying new tool bits, I'd get HSS for the lower price & easier understandability; but if I can tool up these three holders with 10x bits each for less than 60 quid (which seems achievable), then I may as well.

Tion - I've been using eBay for the codes, but I got a bit bogged down in the grades. However, I'm now pretty well ignoring the grade & just looking at the prices...
I found this tool selector:
http://www.canelatools.com/cataleg/tec2/tec-ins-index.htmwhich seems pretty good (and quite interactive); doesn't cover the chip breakers or grades though.