Its not unusual close to trees and hills for the wind strength and direction to vary wildly.It looks to me as if the junk is hard on thne wind in a good breeze while the sloop appears becalmed possibly sheltered by trees etc ashore.
Go to the yahoo junkrig group. Not much use about discussing it here. Most western rig sailors will only be able to pass on second hand information whilst lorcha or sampan sailors will no doubt have experience with both. Bit like asking the pope whether reincarnation does work after all! /forums/images/graemlins/wink.gif
I built and sailed a junk-rigged 30 footer complete with 500 sq ft sail incorporating aluminium hinged battens. As mentioned above, she sailed very well off the wind but didn't tack or point anything like the bermudian or even gaff-rigged boats that I have owned.
The sail was great in some aspects such as not having to worry about the consequences of an unplanned gybe and being able to drop it in an instant. Raising it was more dufficult though as there was a lot of timber, cloth, metal and knitting to launch up the mast in anything like a sea running.
One word of caution regarding the junk-rig enthusiast groups however...it is my personal experience that many so called experts /forums/images/graemlins/ooo.gifwill give advice and encourage experimentation with new cuts etc...just as long as they are not paying. Stick with tried and tested designs and you will have a very workable boat.