I voted for Feb and August.
August seems a good time to have them, but I like the idea of them being spaced apart enough that any necessary saving for expenses can be done.
Look at it like this, you need money for:
Beer
Train
Hotel (unless we go during uni season and you can get lucky - rock city is a meat market btw)
Food
The fact that we are in WHW and therefore tempted to buy shiny new toys!
But I am easy come easy go with dates. It would be good to have two every year and be relatively set in stone with the months they will occur.
The other thing to take into consideration is whether or not WHW will be booked up at that time of year for tournament gaming etc, or if everyone is at games day...