Ok did a test, tried getting the water to a rolling boil with the metal lid, BCB lid and no lid with a Colemans Micro Stove, here are the results:
No Lid
Time: 7 minutes. Pro's: Easy to see progress. Con's: Slow, contents not covered (can lead to contamination).
BCB Lid
Time: 6 minutes. Pro's Easy to see progress. Con's: Lid a nightmare to remove (I had to use a spoon to lever it off and even then it fell into the boiling water. However a liquid could be poured without removing the lid), cannot be used on a fire as it would melt.
Metal Lid
Time: 5 minutes. Pro's Fast, Lid easy to remove. Con's: Can't see progress (but you can hear when it's boiling as the lid starts ratterling).