Graham, you comment on the thickness of lines has much sense.
However correct casting technique can overcome problems with casting against the wind, even with a thicker line. The secret (no secret really) of this is the ability to cast a tight loop.
All sorts of rubbish has been written and talked about regarding long distance casting and the ability to cast against a stiff breeze. It's all about the amount of line area you can put against the wind. Cast a tight loop and you can chuck 20 yards against a gale.
The way to do this is difficult to explain in words. That's why I would recommend anyone who wants to improve his or her casting technique, to spend some time with a pro.
I spent over 20 years teaching fly casting, but I've never done this since I returned to the UK. I used to make the odd bit of cash doing this. But if any member of FM wants to improve their casting, I am available for nowt.
Well maybe the odd pint.
And that mob on other threads think I'm an ultra tight Yorkshireman.