I scored a sport suspension Paralever torque arm (this particular one was from a boxer cup bike, but the GS torque arms are the same length), and had a chance to throw it on the bike last week. This is an interesting mod...
Here is a comparison of the two bars - stock RT bar on the left, 365mm bar on the right:
The initial reaction - the bike definitely sits higher in the rear...and is a lot easier to get up on the center stand:
It is also going to affect the side-stand a little...It isn't a problem in the garage, and I don't anticipate it will be a problem anywhere else, but I suppose I could always add some sort of extension if necessary.
The idea here is that the shorter bar raises the rear end and makes turn-in quicker, making the bike feel more sporty. Does it? Well, I have the luxury of living about a mile from a twisty mountain road, and the verdict is still out after a couple of runs up the mountain, but my initial opinion is pretty good - turn in feels a bit quicker, and especially transitions from one side to another in esses - it rotates more easily. I need to get my Ohlins rebuilt and set up for my weight and the new ride height - and I think overall it will feel pretty spry.
It certainly doesn't turn the RT into an R12S, but I think it is a worthwhile addition, as long as you don't pay a bunch for the bar. I'll have a much better opinion once I have the rest of the suspension sorted - I might even switch back and forth to see what bar feels better, but I'm almost certain the shorter one will get the nod.