1. if you are taking the cable outside, it would need to be protected ideally, shielded if you like.
2. might be hard getting it down, depending where the "dabs" are - you should have a cavity between the brick and your inner wall though, might be able to get it down there
3. it would look crap coming down a corner of a room upstairs, then again downstairs unless you could hide the cable quite well...dont have chimney your not using do you

4. doesnt have to be along skirting board - pull your carpet up get a long enough cable and run it between the gripper and the skirting board to wherever you need it.
I would go with option 4 personally. if done right, you wouldnt see it at all.
of course you could always get a wireless repeater downstairs and not bother with any of that lot