do screws make a difference in mounting wall plate

I think you mean non magnetic, non ferrous, screws.

Toward the end of this thread: http://forum.audiogon.com/cgi-bin/fr.pl?fcabl&1401648535&openusid&Audiolabyrinth&4&5&st100 your topic question is discussed.
I know that Audiolabyrinth (Audiogon user name) has done a lot of experimentation on the topic but I can't find the article.
You could always PM him.

I'm not worried about the screws in your wall plate. I'm more worried about the screws in your head.

Labyrinth has posted impressively about that. Maybe in his tara labs thread.