i've made bridles for both my 9 and 12m kites with no problems and the wear is really good. head down to a sailing shop, there is one at the marina between outer harbour and largs. or even glascraft. i don't know what the lines are called, but they are cored, like the flying lines.
usually go thicker than the standard bridle lines. alot of line wear is from side movement through the pulleys. take your kite in and run the different sizes through the pulleys, look for the best fit. usually about 5 mm line for the bridle pulleys.

while your there get some splicing thread. just sew the loops... and you're done.

There's a little place accross the road from Quinns marine down at the port. They have rolls of heaps of different lines, everything you will ever need, and off memory the line is around 50c a meter!

I popped into Binks on Fri & picked up some German brand of Dyneema 75, so i'll see how that fairs up against the Marlow Excel. The guy in the shop reckons Marlow is an inferior rope compared to the Dynex/Dyneema 75.

Cheers for the feedback chaps.