I'm currently running the "middle sized" bar, and enjoy the difference. I
took the bugeye out for a test run on a long straight road near home and
quickly put it up to ~100MPH. A small irregularity in the pavement caused
the beginning of a cyclic phenomenon that I would describe as hopping from
one foot to the other repeatedly. EXTREMELY scary. I backed off and all
was good. Weeks later, after fitting the small stock bar, same road, same
speed, same bump, but much less of the back and forth phenomenon. I later
upgraded to the 5/8" bar and now I can hit that spot at 100 and there is NO
oscillation at all. The nose is still light and sketchy at 100 so I don't
do it anymore, but the anti-sway bar certainly cured that particular
problem. For around town use I don't suppose it would matter that much.
But if you want to get your money's worth out of a Spridget, put one on.
The problem I've had with the larger bar is its ability to rip apart the
front frame rails at the mount points after a session of "extremely
spirited" twisty driving. After a couple of re-welding sessions there now
seems to be enough weld on the rails that they haven't failed since. I'd
say that if you're going to fit the bigger bar, seam welding the foot or so
of frame rail with the mount points would be a good thing.