The voting will be very interesting. As of the end of March, there were 6211 members of LonCon3 and they're on track to break 8000. That's the largest WorldCon in ... ages if not history. It's based in London and 2177 of those members are from the UK.
The largest worldcon was in 1984 LA Con II with 8,365 members.
The other cons that have had numbers greater than 6,211 are (unless I've accidentally missed one out) in ascending order of numbers:
59th Con 2000 with 6,269 - Millenium Philcon
64th Con 2006 with 6,291 - L.A. Con IV
41st Con 1983 with 6,400 - ConStellation
51st Con 1993 with 6,602 - ConFrancisco
53rd Con 1995 with 6,703 - L.A. Con III
62nd Con 2004 with 7,485 - Noreascon 4
47th Con 1989 with 7,795 - Noreascon 3
So basically Loncon3 has yet to exceed 8 other cons in terms of numbers.