There's no such thing as 4.2. You should get the HD content on 4.1.
We had two subchannels for awhile, but shut down the SD simulcast a few months ago so 4.1 is the only one you should get.
(incidentially, last week we hooked up the 5.1 Dolby audio encoder - some of the Olympics will be in 5.1 surround, along with some other NBC programming - we're hoping all is OK with the audio but if it isn't please drop me a line at firstname.lastname@example.org
The 42.whatever kw power we're running is the maximum permitted on VHF channel 10. VHF "gets out" a lot better than UHF for the same power. Among analog stations, the FCC limits channels 7-13 to 316kw; UHF stations are allowed up to 5000kw. They figure both stations will have the same coverage. Our 42kw on channel 10 is analogous to about 600kw on channel 27.
At my location in Cheatham Co., our signal is at a par with WKRN's 900kw on channel 27. (WKRN's DTV works a LOT better than their analog!) WTVF comes in second with their 400+kw on channel 56; then, WB on channel 23, then Pax on 36 (there's a lot of interference from Kentucky on 36 up here), then PBS on 46. Fox and UPN on 15 and 21 can be seen under good conditions but it's tough. I've seen the religious station on 38 and the home-shopping on 44 but both only once. I know the religious station on 51 is on with their 400 watts (seen while visiting the base of their tower!) but not a hint up here.
(but UPN has a directional antenna and has less than 1kw in my direction. A 1kw analog on channel 21 would be completely invisible at this distance!)