John, number one I would NOT install 1.0 kg fork springs and not change the rear spring also or IMO the bike will be worse off.
The rear is already too soft and installing 1.0's in the front will shift a LOT more weight to teh already too soft rear end.
Outside that, looking at just the forks: installing 1.0 springs will slow compression & speed up rebound, so IMO you would want lower weight oil on the comp. stroke and higher on the rebound side to slow down the bounce back of teh 1.0's.
On SAG IMO the only real way to know if the springs are right is to have correct FREE & Rider sag, not one or teh other.
BR