I heard from SR500 guys that dual discs might be too heavy for a such a small bike, especially the 320mm ones, cant argue with the looks though. Not tried it myself yet. Waiting parts to arrive and will go first with 1 side.
Meanwhile the biggest challenge I face is to get all the small bits that go with SR500 front (axle diam is different to XS400). Its easy to buy a SR500 wheel on ebay but sort everything else is more pain.
For anyone still considering going with SR500 /XS650 fork and wheel, here is a link that might be useful to give you an idea of what you possibly need:
https://www.cmsnl.com/yamaha-sr500-1978-usa_model8661/partslist/E-06.html#results
I also like the fact that the SR500 tubes are thicker just looks bit cooler with 19inch wheel.
Out of interest, can anyone confirm if the xs1100 possibly also xs750 have same axle thickness as xs400? Found a post from user "cafe from paris" ... if i remember correct he claimed that he left xs400 forks and just went with xs1100 wheel, which was just a straight forward wheel swap?