Lou Deeter said, "...
but I do believe that SLX was actually about 30 grams heavier than the SL frame, given the same set of conditions--only change of tubes."
This is exactly to be expected as they were the same metallurgically, but there was internal rifling inside the tubes, e.g. headtube and near BB on the SLX, hence the extra grams.
Ken Wehrenberg, in beautiful Hermann, MO