I know a lot of people will shout me down for this!! We ourselves use a 1250 watt machine (there's videos on our website) and have used up to 4200 watt machines. To be totally honest we've never noticed a difference, the 3000 watt machines are slightly quicker but they take longer to set up and overall we've found we take the same amount of time. Another thing we've found and we've 2 jobs alone this week is access, we couldn't have got a 3000 watt machine through the garages to the job but our little machine we just carried it through.