From my experience, matched packs tend to last longer.
The reason for my opinion is this: Matched packs have similar runtime, IR and charge characteristics. This generally means that all cells in a matched pack will reach their peak charge in close proximity of the other cells. This reduces the risk of over charging cells, which causes damage. They will also discharge at a rate similar to the other cells. This reduces the risk of reversing cells, which causes damage.
I agree that the manufacturing tolerances on cells has really reduced the number of truely bad cells. I think that purchasing loose unmatched cells and building packs will definitely give you all the battery you need for normal weekend club racing. The need for high dollar packs for weekly racing is way over-rated.
Jeff Gilligan