On 129 (and Eastern Arc) anything above mid to high 40s is great. On 110/119 anything above mid to high 60s is great. Signal strength does not affect PQ. Signal strength of 10 or higher is necessary for satellite lock. A channel with a (steady) 11 will look as good as a channel with 50+. The reason to aim for higher signal strengths is to minimize effects of rain fade during storms. The higher the signal strength, the more leeway you have when storms come through. However there is a point of diminishing returns. Striving for ultra-high signal strength will only gain you an extra 10 seconds of sat signal during a heavy storm. Thus the reason why people say mid-to-high 40s is great on 129/EA and mid-to-high 60s is great on 110/119.
By the way, 110/119 are no more powerful than the rest of the sats, they just use an (older) form of modulation that is compatible with old (outdated) standard-definition receivers. The set-top boxes measure the signal strength of this modulation differently, however mid-high 60s is about the same as mid-high 40s on the HD/EA satellites. Sooner or later Dish will get rid of all the obsolete receivers that require this older modulation scheme and will upgrade all of the 110/119 transponders to the new scheme. This will make the signal strength "lower" on the sats but again, mid-to-high 40s and up is fine.