Hi Rob, welcome to the forum. The FAQ ("how are my stats") takes a stab at this age-old question. Folks throw around '1k' as reasonable number, but for those that have played 10x that amount are far too familiar with swings that can extend to this 1k mark and beyond (see bigjoe's chart in the 'SNGICON' thread).
Basically, we're never 'there' [img]/images/graemlins/wink.gif[/img] ...but after a thousand or two, you should have at least gained enough experience & comparison through observation I'd think, to have a decent feel for how you're doing.
Check out RVG's ROI simulator here:
http://forumserver.twoplustwo.com/showfl...rue#Post5736082
...can be fun to play around with the probability stuff.