Last night I eventually managed to get the board out on the sea, 20 mph cross off shore with a 6.0mtr and away we went. Had it blasting at speed when it really got going and with some heavy pounding over some small chop there didn't appear to be any problems with the repair.
This afternoon when I had time to wash the board down and check it more carefully the repair has so far held well.
here's a pic prior to getting wet yesterday, looking lovely and shiney with 3 coats of varnish.

My advice to anyone in the same boat, got some damage and thinking about a DIY repair would be to do it. Especially with the advice and help from sites like this.
Happy days!