I've been running a 65" Hitachi rear projection for over 6 years. It's been a great TV. Like you, I originally had it in a large room with the seating far away from the TV (over 15 feet). It was a room that traditionally was darker with limited windows (hence bright sunlight). Worked awesome.
Then I moved. Seating is closer to it now and a whole wall of windows that face NW so setting sunlight is plentiful. You are right about it not being as bright as a plasma or LCD. What we did was put some fabric blinds on the windows. They are not black-out blinds, but knock the sunlight down. It makes a big difference. Still very light in the room via the sun, but it made a big difference in screen visibility and reflections. It really isn't a problem viewing the screen anymore.
My major issue is my rptv is older so it's pretty deep. The front of the TV sits a good 38 inches from the wall. That's a lot of floor space one is giving up. Especially in a room much smaller than one in the previous house. But that's life. I'm looking to replace it with 60"-65" plasma to cut that back but the CFO isn't convinced or at least I have not agreed to her terms.
Enjoy. Size does matter... for TVs.