Hi Tom
I've been running the following set up;
Front - 4x55 with 30wt and a Green Spring (plus 4mm of internal limiters to get the correct droop)
Rear - 4x54 with 25wt and a Pink Rear Spring
I've run this on grass and astro and feel that you may want to numb the front a little more for hi-bite astro, so maybe go to a blue spring on the front or go up in oil a little. I've never been to southport, but have run this shock set up at stotfold, epr, kiddy just to name a few tracks I have run this set up at (if that at all helps
).
HTH
Chris