Kevin,
Works for me, but another option - maybe let the Aussies start with next season's crop. I know if my goal is to only grow the largest single tom, I'm gonna treat that plant differently from not long after it is transplanted. Not that they can't compete this year, only that they "can" wait and be a part next season. Run the contest until May 1, 2011.
I do see arguments developing about largest fruit by type - what exactly is a "cherry tomato" vs. a small medium size. I have a Legend plant (by all means should be medium size, slicing type) but thanks to the lack of sunlight here the past month, it is completely ripe and just a hair bigger than any cherry tomato I've grown. But biggest (or heaviest), regardless what type, in not open to argument. For those divisions, I would go with best looking plant or best looking cluster of maters. Riesentraube has great clusters, sometimes 30 or more ripe cherry toms at a time.
Another category, and we choose to enter it or not, is highest production per plant. It is a bit of a pain, but I've done it with a volunteer cherry-type and isn't all that hard if one has a decent scale. It was not a good year, but I ended up with just over 21 pounds of maters from that plant. Had it been a contest, I probably would have had 26, maybe 27, because I left a lot of toms on the ground as I only picked them twice a week at most. The problem with this (there's always a downside) is that those growing an indeterminate plant in a long-season climate should get more pounds per plant. But that's fine by me. But if I read that someone got 54 pounds of edible Celebrity tomatoes, even if they had an eight-month season instead of my 5.5, I'll know it is a very productive plant.
My 2ยข worth - with perhaps the exception of largest mater, I feel points ought to be awarded like on "Whose Line Is It." You get them for winning, but they don't count!
Mike