I built a DB4 antenna for about $20 and an hour of my time that pulls in almost all yellow and lite-green stations in my area, including hi-VHF channels 8 (virt 8.1) and 10 (virt 11.1). It is based on the plans here:
http://m4antenna.eastmasonvilleweather.com/index.html and looks like a CM-4221HD antenna, but is specifically designed to receive Hi-VHF channels too. Mine is mounted in the attic now too. Originally it was in an upstairs bedroom. All I can say is I am amazed at the difference 8 ft of height makes to reception.
I believe the CM-4221 only pulls in UHF. I'm just under 20 miles from the transmitters here. Since you are closer, there shouldn't be any issues unless you have metal siding or a metal roof or a big barn in the way of LOS.
I see your are referencing real channels, not virtual channels. Good.
This post
http://www.dtvusaforum.com/dtv-hdtv-...ata-4-bay.html should help you select characteristic for a home-built antenna.
My cable run is not as long as yours, but with the signal strength you are getting, that might not be important. You could always place the HDHR closer to the antenna and only run an ethernet cable all that distance, if loss is an issue. I have an HDHR too.