Hmm… certainly 6 small against average players, even pretty good players are usually shit at it. (Like me circa 2013!) Even though I’m a little rusty on 6 small these days, I’m always taking points off good players with it (sometimes it backfires but yolo).
When it comes to geeks, it massively depends on your own strength and their own strength. Against a super maths nerd I’ll go safe with 1 large (I actually have a pretty good record at dicking maths geniuses with 1L), against a 4 large expert I’ll go 6 small, against a 6 small player I’ll go 4 large. I’d say that while I’m no maths expert, I’m one of the few players who is very good at both of them.
My philosophy (in the words of Louis Van Gaal #neverforget) is that easy 4 larges are easier than easy 6 smalls, and difficult 4 large are harder than hard 6 smalls. Wahey, hard!!