Nice one! Problem found, it was the boing bag 2 rom update!
I'm now getting high 20 fps.
Pixeltest result
VRAM->RAM : 5222.44 K/sec
VRAM->RAM(16) : 6279.73 K/sec
-------------------------------
Conversion : 9668.25 K/sec [output bandwidth]
Conversion : 4950142.18 pix/sec
Conversion attained 99.34% copy speed
I haven't a clue what any of this means but I guess these figures would be about right?
Thanks for your help guys. MUCH appreciated