If you are trying to get the brightest picture, you need a High Power / High Gain screen. This is a great screen even if you don't need the extra brightness, but it will do a lot more for reducing ambient light effects then just upgrading your projector. You can get a 92" one for around $300, or a 106" for about $400.
BTW, the hc3800 is the best picture quality wise dollar-for-dollar by far (and it comes with an extra free lamp), so the real cost is about $1,000, but DLP's with high offsets cannot properly be paired with a High Power screen.
Therefore, out of those choices, my recommendation would be the Epson 8100 or 8500ub paired with a High Power screen. You're going to get a way better image with ambient light if you change your screen. Keep in mind that the Epson 8500ub commonly has issues but the Customer service is easy to deal with to get a replacement, but that said you may have to return it a couple times to Epson until you get a perfect unit.
The 8500ub is worth the extra money if you have the extra $1000 to waste. If you want to save some money, wait until next year's models come out in about 4-6 months and you can often get the previous generation a few hundred cheaper (sometimes even less).