Thanks Dan. I suspect the non-linearity is not news to Gilles - the french boys did a lot of testing in the early days, and I'm sure they've already investigated this in depth.
I'll do as you've been telling me for the last few posts, and set up a few fixed-speed foams
Appreciate the detailed responses - it's helped me gain a much deeper understanding of getting good results from GMFC.
Oh, and I tried the latest version of GMFC PE but it crashes when I go into the Foam Management screen (under Win 7 64-bit). Back to v3.89 for me