Thanks windyrigg
Made another version of the windshield this afternoon, drilling the pot stand holes this time (4mm drill). Much neater and stronger than the holes I get using a 4" nail, which are prone to tearing at the corners, a point of weakness. And 6 air holes punched around the bottom edge rather than 4 (the Speedster windshield has 6 indentations along its bottom edge). Not sure whether that makes much difference in practice.
Tested with the Speedster burner (inside), 10 minutes to boil 300ml water, using I would estimate about 18-19ml of meths.
The 50ml plastic bottles that I ordered from Swindon Composites via ebay are excellent: light, tough plastic, close fitting lid, and they make it easy to measure out a 25ml fill of the 30ml burner, half a bottle in other words.