During daytime viewing a projector which can achieve 10,000:1 contrast ratios will be reduced to levels below 50:1 (no, not joking) so the most important specification is the one you will be hurting the most under this viewing scenario.
That said, you really want the lumens since added lumens, while they raise black levels and lower all around contrast ratios will combat ambient light far better than anything else. In fact, I would likely steer away from the HD70 in favor of trying to get the Panasonic AX100U which should deliver a fair bit more overall light output and then still be adjustable enough to offer lower light output with higher contrast after dark.
Now, the screen is a different story. Absolutely the best screen I have seen was the DNP black screens. For lit room conditions, nothing is better.
And you can't afford it.
So, I would go with a moderate gain screen as a better alternative. Realistically, you aren't going to do much with black levels unless you go with a positive gain, grey screen which both enhances black levels and brightness at the same time. I believe Draper, DaLite, and Stewart all make screen materials like this. But, if your budget only affords you Carada, then I would go with positive gain over grey screens in a second. A 1.4 gain screen will help the projector deliver more light back to your eyes in a higher than normal lit room which should be sufficient to allow you to enjoy gaming/etc. during the daytime.
For me, it wasn't enough and I went with a 50" plasma behind a 106" manual screen. During the day the screen went up and the plasma came on. It solved the issue without making me rebuy a lot of gear.
