if you're going to put the mics at different distances from the source you're probably going to run into phasing issues. Of course you could align the room mic tracks to the close mic tracks to get them in phase with each other.
What I usually do when I double track is 1 close mic (or usually 2 close mics in Fredman style) and one condenser mic right next to the cab aimed into the room (in the direction the cab is facing) Since it's at the same distance of the source you won't be likely to get much phasing problems. I do usually have to invert the phase on the room mic track, since it's aimed in the other direction than the close mics.
In a mix I usually have the mics like this:
git 1: close 100%L, room 100%R @ -9 dB
git 2: close 100%R, room 100%L @ -9 dB
sometimes I don't have them panned so wide. Then it's more like this:
git 1: close 90%L, room 80%R @ -9 dB
git 2: close 90%R, room 80%L @ -9 dB
I usually don't use room mics when quad tracking because I think it gets too dense and full but for heavy rock stuff I do often quad track the choruses and some other parts that need it. Then I usually do something like this:
git 1: close 90%L, room 80%R @ -9 dB
git 2: close 90%R, room 80%L @ -9 dB
git 3: close 100%L, room 95%R @ -12 dB
git 4: close 100%R, room 95%L @ -12 dB
listen to the second song on my site to hear what I mean:
http://www.xpzsound.nl/mp3/ (Tenement Kids - Strain) the extra guitars kick in at 0.35, you'll hear the effect then.