I I haven't tried messing with display modes on Workbench, i don't see the point because like you say, most games will run lowres.
There is a picture coming thru on scart, it just rolls and there doesn't seem to be any way to stop it via the TV.
Annoying because it will work fine on my mates Sony Bravia TV over scart and it does look stunning!
I am going to try a scart to composite converter, see if the front TV ports have better luck.