Simsi - 9:13 pm on Jul 2, 2013 (gmt 0)
I've got everything at around 13 or 14 size, mostly Verdana. My only concern is that it might look too big on an iPhone or other small mobile phone. Otherwise, I think bigger is better.
Shrink it a tad and use line-height to space it. That works well from a readability angle.
On the OP, my thought is that *if* there is a correlation between font size and ranking it is only that 9px was negatively impacting rank and 13ps is deemed acceptable.