OK as of an hour ago I now have applied my GeoIP blocking solution to the signup page on my production Moodle server. Now for some historical metrics before I remove all the disabled spam accounts I have collected.
Since enabling the ReCAPTCHA I have had 526 spam accounts confirm via email in the past 51 days, so an average of just over 10 per day. The spam accounts list random countries but 4 of the accounts listed the country as Canada (which is the country where I am located), making the spam accounts slightly less obvious to filter out.
I did have some notorious spam email domains listed in my "denyemailaddresses" setting (.info .co.uk mailnesia.com frenchcuff.org) but with my new setup I will be removing them altogether.
I will check back with this forum in about a week to let you all know how things are going, and will document my solution if the upgrade proves successful. FYI, my production server runs Linux (Ubuntu Server 12.04 LTS) and my documentation will reflect that.