I just like to add that if you experience wobbly feeling driving at high speed on a say very open area NS highway, chances are that you could be encountering wind drafts, thats why they installed wind socks on some stretch of the NSHW.
you don't have to go far to experience that, even in SG, especially recent weather has got sudden gusts of wind, travelling at 90Km/h along TPE or changi coast roads during early evenings, u could feel the wind pushing your car so badly that U need to adjust your steering wheels to correct the car heading.
So keeping to your speed limit is important on open areas of the NSHW, a strong gust of wind can make a lane filtering potential hazard