only SLX, TSX and SPX had rifling or "helical reinforcements". SL does not.
Yes, for the frame. For fork steerers, some of those also have rifling, and I'm not sure if they are classed as belonging to any tubeset. My non-SLX frame has a rifled steerer tube, and I've heard this being referred to as an SL steerer, whatever that means...
Even if it wasn't rifled, there isn't much difference between SL and SLX. The amount of flex will be more greatly varied by the size, and on top of that the geometry is much more important (of course).
Yes, for the frame. For fork steerers, some of those also have rifling, and I'm not sure if they are classed as belonging to any tubeset. My non-SLX frame has a rifled steerer tube, and I've heard this being referred to as an SL steerer, whatever that means...
Even if it wasn't rifled, there isn't much difference between SL and SLX. The amount of flex will be more greatly varied by the size, and on top of that the geometry is much more important (of course).