Two people are currently arguing about this. One is saying with the timing retarded by 8 degrees, you'll have a runability problem at any speed; the other is saying that you won't notice the issue when driving in town(25-30mph) but will notice it when trying to travel at highway speeds(55-70mph) and that there will be a loss of power.

Personally, I feel the higher the speed the more timing needs to be advanced.
Retarded sounds like a tractor.
That's my opinion, I'm sure I will hear feedback, that fine, love to learn.