Hiya.
As others have said "Well if theres no wind? the use/non use of a windshield is mute." is not correct at all. The short answer to your question is "how long is a peice of string". That is not being flippant, but you need to add more detail to your equation. If however, you used a lightweight wind shield then the answer will be yes, but yet again you will need to qualify how many uses of the cooker you are referring to. On cookers such as home made meths stoves, a shield of the caldera cone type can add over 25% efficiency to the stove, thus making it very worthwhile very quickly (for my own use, a windshield reduces fuel use by 12-25% depending on stove type).
Hopefully you compare various lids, as for example my ultralight lid and shield for my ultralight pot only weigh 20 grammes together, while my lid for my dutch oven weight a couple of kilos, thus presenting totally different scenarios.
The test conditions (if you have not looked them up already) should be indoors with no breeze present, in a room at twenty degrees and water at twenty degrees C too. Although this is hardly ever likely to occur in the outdoors, or 'the real world' it is the standard test set up stove/pot manufacturers use (which is why their claimed boil times seem a bit far fetched at times).
If you stick to the above criteria then variables such as efficiency of butane V propane V butane/propane mixes at differing temps can be discounted, and purely the differing weights of the fuel need to be addressed.
It is also a good idea to stick to using the same pot for measurements, as I am sure you already know that various metals have different conduction abilities, although this does bring on an interesting twist to the experiment. It could be interesting for you to measure the difference (if any) of boil times when a pot has an alloy lid v a stainless one V a titanium one.
One other interesting point is the difference a close fitting lid makes as opposed to a loose one (its quite different!)
Going back to windshields for a second. The added extra a windshield can give you in increased convection or flame contact to the side wall of the pot, rather than reflected heat (radiation).
Of course this should lead you to also consider the effect of the width of the pot you opt for. A tall narrow pot will have an increased benefit from a lid more than a shallow wide based pot will.
The closeness of the windshield also makes a massive difference to the weight/volume of fuel used to boil your given amount of water, as will the shape of the shield (as in whether it is vertical or cone shaped).
Last but not least, and not directly relating to lids, but it must be remembered that gas stoves are not at their most efficient when on full power setting. It will be found that a gas stove operating at fifty percent capacity will take a bit longer to boil your water, but will also use less fuel. This is important in that if you use a gas stove for your test, then you need to mark off the power setting to keep it consistent, but also bearing in mind the pressure drop of gas as the cylinder empties (which will also affect boil time).
Just a few thoughts
