They are very good aeroplanes. Rugged, good visibility, great load carriers and forgive much. Even their best friend wouldn't accuse them off being fast or light on the controls. BTW, slats extend around 110 kph. I've usually got full flap and engine to idle by then. It will probably make a slight difference to slat extension speed but I've never bothered to look. Do your own conversion to your preferred units. Then just fly enough nose up that they don't retract again until you are ready to round out. Close your eyes and pull hard. Return for the next glider while opening the canopy for a breath of air, setting flaps to half and doing whatever you need to with the fiddly bits.
maybe don't do that if it's not flying right though.....
Seriously, if it rolls into a turn at 70 knots something is very wrong. Where are you based? I fancy a bit of a cross country with the not a Cub.