Top 5, 10, 15, 20, etc...

I was wondering if anyone had done any comparisons when it came to 'top 10' type listings on TGPs and Link Lists by way of seeing if a top 5, top 10 etc list actually generated more clicks than another?

We're in the process of planning out a new network of niche specific TGPs and Link Lists, primarily for our own in-house projects but we're eventually going to open these sites up to submissions from others and was just curious if anyone had any feedback on whether including a list of the top 5 sites in any given niche had worked better or worse than a top 10 list of sites in any given niche?

Im seeing that the most common thing to do is list a top 10 and im wondering if that is for any statistic reason or just because it is the 'norm'?

Your thoughts?

Regards,

Lee