I'd say MDG is fine, or a Dragon 25kCFM
Check CFM ratings...
Wow MDG's site blows right now.
For outdoor shows, you only have two choices... High laser power or high
volume smoke upwind... Preferably both...
If it's enclosed like a stadium you could get by with smaller.
Oh yeah, there's a few good photos of the Big Max doing some over river
shows on the net... Basically particle size isnt' important for outdoor since fog
dissipates so quickly.
--
addendum, I've just went through their site and they're not listing any of
their huge foggers on there... So I may have to retract the MDG... They
still make nice oil based hazers though.
The thing to look for in a classic fogger is the heater element, you don't
want to have to wait for reheat... I'd say 1500-2000W heaters for outdoors....
Oh, and don't run the outdoor foggers indoors
I learned that the hard way.