I've always wondered if the XT500 and the SR500 had the exact same engine. I had a 78 XT500 and loved it, but couldn't keep the valves in adjustment (I think the valve stems were soft). They never did find the problem, but Carter's Yamaha (family friend) gave me a new SR500 to ride while they worked on the XT. The SR was SLOW compared to the XT. I figured there had to be a difference in the cam, compression, or something & didn't think the difference in performance was attributable to gearing alone. I wound up trading for an XS500E because the SR500's performance was such a disappointment to me & I really did want to like the SR500.Beautiful bike.
I had an SR500, same engine. Loved it.