Many thanks for that help, you see this is where lack of knowledge really bites me.
As I know not what is right or wrong, I can only follow stuff given to me here and there on the 'net. So far this advice has been to cut at silly fast speed with full-on acceleration and as much power as I have. That is what I was testing when I spotted this effect. Obviously I had pushed my parameters too far and not realised.
My previous cuts were exactly where you just said - around 3300mm.min!
I was going faster to see if it reduced dross (easily tapped off) as I had been advised. In the end the dross got less but harder so counter productive effect. This was with standard consumables.
Even at that 236ipm rate, the little table still managed to make that cut without losing a step which I feel is a good thing, I will retune it this week and reduce the speeds again a fair bit back into the real world.
BTW the book recommends 10,000mm/min which just seems stupid fast and there is no way that could be attained on a table that is only 700mm square without some serious G force effects, it would probably tip over on each corner
Thanks again, it is real-world figures I am searching for, but bear in mind I only have 30A to play with.