" I thought the IS 300h drove much better than the GS300h, also felt more screwed together than the GS "
Well I beg to differ, after 3 years with a 3gen 250 have now, admittedly after just 250 miles in my GS 300h I find it a much more refined drive, have just arrived back after a little drive through the lakes and found it handles ( for a large saloon ) very well and the ride is much smoother than the IS, its also beautiful finished inside.
My GS is on 17 wheels.