It's a balance between weight, rigidity & strength.
No doubt you could lighten the slx further but you would lose rigidity. You could make it even more rigid but you would add weight.
I've got the very first MKI slx & the very latest. The MKI was a "tiny, tiny" bit more rigid BUT heavier & with a larger base diameter. The newest one is lighter, slimmer base diameter & almost as rigid- the difference in rigidity is hardly noticeable, but there if you want to be really picky.
However, the latest slx is much the better version IMO, overall easier to use.
If you change the materials & technology then you can get even closer to perfection- that's where the Xtreme takes over!
