i dont have a w58 in my supra, but i have had 2 celica's wiht w58's, and the shift qualitly is far better in the w58, it's like shiftin into butter, while the r's i have driven you feel the engagment of the syncro and the gear, feels like it goes into gear twice, where the w58 is just smooth,
even my rebuilt in spec R shifts far better then my brothers R, we have the marilin bushings in both cars, you can still say a worn out w58 shifts smoother.
if you have low power qoals stay with your w58, other wise the r154 has seen 843 horse, from nates car, and 814 from duanes, now take it you dont want to abuse the 1st to second shift when making over 400 horse, and close to the 500torque mark, it'll snap the thrust washer..