great to point that out keith. yes so for normal street in sydney roads, the lower than normal spring rates given by tein (for example), it is best to go for a much lower spring rate.
however, reading that article, there is uneven weigh distribution between the front and back compared to the rs200 with the is300's; and is200's would be the same.
now tein has spring rates for their coils for the is300, and i assume (without emailing tein) have adjusted their spring rates according to the rs200 because of the uneven weight distribution.
so having said that 5kgf/mm front and rear may not be completely optimal (as the fronts need to have a higher spring rate). the mech who quoted 5 all round has vast experience in rs200's so would be familiar with the rs200s even weight distribution. and it makes sense now why he quoted 5 all around.
ill let him know the is200's weight distrubtion (after some research) and he should be able to recommend a higher spring rate for the fronts for the is200.
thanks for that keith!