I doubt it - mine came in at 1490g too. I've never had any trouble whatsoever with freehub wear on my three pairs of K's depite masses of terrible English weather.
Three clubmates and I had great enthusiasm for the new 7800s this time last year. All of us have now sold them and gone back to K's.
I owned Ksyrium SL2's last year, had 5K miles, I loved them. Mine weighed about 1560g, don't see how you got a 1490g set, Mavic never has wheels lite as they claim, I'd like to see yours on a scale. I've never seen a set lighter then 1550g, and I have weighed over a dozen sets in different shops at different times. 100g lighter then DA? I don't think so, maybe 40g tops.
I am now riding DA 7800's and they feel much more lively then they Ksyrium SL2's, not to mention the have signifcantly lower rotational mass. DA wheels have VERY heavy hubs due to large bodies and large axles (15mm both front and rear). Front hub is in excess of 170g, rear is around 270g. Dura Ace wheels also have a MUCH more aero rim, hidden spoke nipple and an aero shaped rim.
SO.....
Unless your using campy, the obvious choice is DA 7800 as they are superior to SL2's.
Don't get me wrong, I love the SL2's, but the DA's are better. If you ask me, alot of people out there just buy the Ksyriums because they look cool.