I honestly don't think your final assessment affects what loot you get once it's established you're getting loot at all. I've gotten 4 coins for a 5k assessment and 1 coin for a 9k one.
I mean, the loot spreads across several 5500ish assessments for me were so random that I can't imagine getting any sort of predictive sample without dozens of people recording their results for months, and for what? Coins come consistently enough that if you stick with WoE, you'll finish your weapons, period.
Probably the best thing you could do is hang on to any of the rare drops you get that are not likely to AH for very much, or even buy them off the AH if you're that desperate; as far as I can tell you always get five pieces of loot from the chest, so having a Rare item in your inventory ought to remove the possibility of it loading for you, Treasures and Tribulations style.