I too had read that the RF was different on the III but when I got mine, instead of the "vernier patch" described on some sites, it just had a fuzzy-edged round spot. So maybe there was a production change somewhere along the line with the MkIII to the improved version (if mine is representative of the improved RF, I'd hate to see the original). If it's any consolation, it's considerably better than a Nikon S3 Millenium...
One thing though - the II and III have a shutter lock around the release button on the front plate which is lacking on the original version and (IMO) is extremely useful to prevent accidental exposures when you only get 8 shots to a roll! But if I had a really nice GW690 I would probably not "upgrade" it just for the lock.