Thanks all for your replies,

Steve,
I can tell you that a 21sqm spinnaker looks HUGE hanging off the front of the Taipan. It's actually quite awesome and has a large grin factor - a large grin factor in 5 knots... I suspect a large terror factor in 20 knots!!!

I didn't actually choose the spi size, it came with the boat. Trevor Brown who owned the boat before me sailed it Cat rigged with this spinnaker and launched it off the tramp on his own! He tells me he was unbeatable in under 8 knots, even by the Taipan 5.7's with spis. I believe him.

I think I might be in for some extreme sailing in the future

I'll experiment a bit with luff tension and sail a couple of races to see how she performs then I'll consider getting the luff recut if necessary.

Rob.