I fitted Ohlins 8.5 N/mm linear springs, I weigh around 13.5 stones (86 Kilos).
Really pleased with them they have been in the FZS 600 for a year.
8.5 N/mm equates to 0.866758781 kg, so they are reasonably close to .90 kg.
My guess would be you could go a little heavier, maybe 9 N/mm would be better, if you can find them, especially if you carry a pillion often and or luggage.
9 N/mm equates to 0.917744592 kg.
Let us know what you decide and how you get on.
Tom