Thank you Sam-Q for your reply.
So I removed the 3.1kg springs and put back the 5kg ones for the meantime to stop the scrubbing. But to my surprise, the car feels so much firmer to drive. Even better than before.
Well, I've had some mods done...eg equal length 4 links, fitted pillow ball bushes on both ends of the panhard rod, coilovers [brand names faded off~ don't know who made them] etc. I admit I prefer how she feels now... but I'm still saving up for the 4.5kgs.
Unfortunately I don't know what rate the front springs have, but there's no scrubbing at all [car sits low] my guess is 7~9kg
Here's how she sits