Larry Bray is about 5-9 and his record distance sling is/was 51" as I remember (look around the site and you'll find its length documented).  After watching him throw a golfball 400+ yards (estimated...  it cleared a forty foot fence at 300 yards and two witnesses said it was still rising when it went over that fence) I would say the length is important in such a Heculean effort but the technique is probably more important.  I was there and watched it and my mind is still trying to grasp the reality of it... it was unaturally natural...  his whole body from hair ends to tips of toes seemed to be focussed and directed into that throw... but he did do it with a 4 foot+ sling length.

GOW

if you mean the one in the 'best long distance technique' thread - then yes. That's larry on the evening of the last day being made to throw for a couple of local lads who turned up late.

He was using a fairly long sling all weekend - so I suspect it was that length or thereabouts.
I know I couldn't do anything terrible useful with it.

I tend to rely a lot more on sheer brute strength and arm speed :-)
(hence the knackerd elbow lol)