The way i look at it Ali, is there's a happy medium. Too light is no better then too heavy, with the word "too" being dependent on the distance and horspower involved.
My thoughts and explanation on it go like this:
1. Take a duckpin ball, a softball, and a wiffleball(holes taped over), these will represent similiar areos.
2. Use your dominant arm at full strength each time, this will represent a common horspeower used.
3. Throw each ball as hard and straight as you can and see which goes the fastest.
My bet is the softball.... and because it's a happy medium in weight.
Too heavy may do better in a long distance headwind(simliar to Bonneville?).
Too light may get there quicker in a shorter distance(similiar to Maxton?).
But there is surely a better choice then the other that depends on the other factors... IE: how much horsepower, what distance it needs to pull itself through, how long it has to get there and the density of the air it needs to do this in(and this is without even taking traction in to consideration). In other words, a very probable changing set of variables(year to year and venue to venue) will have an effect on some level also.
I once thought about something like a set of wheels that would spin up easy for Maxton, and then have some thick bolt on perimeter rings for the salt? A second set of wheels may be a more viable option though.
I may be be wrong alltogether.. but it's been my thoughts for awhile and I'm sure I still have plenty of time before it's something that will have any beneficial relevance in my world(especially as I've never even been on the salt yet). But since you asked I thought this might be good time to get other's thoughts on it too.
Todd