I have a fixed position 6 foot dish that I use for the 4dtv channels on W5. No problems here, never goes out. Maybe others could comment on movable dishes.
My 4DTV is on a 7.5 footer, and it gets excellent reception across the entire arc from 58w to 137w. The only satellite you may have trouble with would be W1 -it's skew is different from the others, and some say the HBO's on G1 are hard to pull in with a smaller dish, although I haven't had any troubles there with the 7.5. I do have weaker signals on some channels on W1, but I run an LNBF. If you use a polarotor you can compensate for the 20 degree difference in skew on that satellite. Hope this helps.