The 5030, or the Sony HW45ES are both very high contrast model projectors. Both have similar brightness.
It should be noted, and is of extreme importance to understand, which I'm sure you get if you do photography... A projector is designed for use in dark spaces. You can't achieve a black level any better than what the surface you are projecting onto appears like without the projector on. Then, the projector adds a bit of light on top of that. (blacks aren't quite black) The typical goal, under normal florescent lighting is a 12:1 contrast ratio. That's far below anything advertised, and has nothing to do with the projector, and everything to do with how much ambient light is in the room.
You raise the black level and you need more light to compensate. You get more light with a brighter projector and while that projector gives up black level, it doesn't matter if the room is bad.
That's why business projectors and home theater projectors are extremely different from each other.
That said: In a classroom you can typically turn out the lights, or most of the lights. You aren't going to be in a 'typical' office environment. That means you can easily go to 100" or larger with pretty much anything. The Epson 5030 or the Sony HW45ES (my preferred model) can do it quite nicely. They have better blacks, which you won't notice until you are in a better room. I might still stick with the Epson 3700 which is brighter and despite the lower contrast in a GOOD room, it will have better contrast in a weak room due to the increased brightness. It may achieve about 50:1 contrast, which is very good in a somewhat lit environment.
Please take a look at this:
http://www.avintegrated.com/lighting.html
That's about 300-400 lumens on a 106" diagonal grey screen, .8 gain.
For a home theater, the Epson 5030 and Sony HW45ES really need a proper space to do their best. Dark walls, dark ceiling, dark carpet. Zero ambient light.