For install the 3.9 WB: try if you will. It runs on a 1200 ks3.0 with 030/25, but will suck! Slow as hell.
No way "slow as hell". The most common source of the slowliness is the new exec.library which is written in C and in some rare cases it is loaded in Chip-ram which produce a big slow-down.
Another smaller source of slow-down is the new ram-handler, but you will hardly notice anything if you don't use the ram disk much.
So, if you choose not install these 2, i don't think that you get a slower than OS3.5 system! I use to run it on the same card that amazing is using, i should know.
I just notice it. KS3.0 you say? I suppose that you softkicked a 3.1 ROM image because OS3.9 won't work properly otherwise.
If you like a better screen,
:-?
funcionallity,etc; try 3.5
I think it's objective to say that WorkBench 3.9 is more functional. Especially after the recent updates on Aminet which are available only for WB3.9, iirc.
and make some patches on then (try Aminet).
Patches are inevitable eitherway.