im the same.my frame came with a 600 i really need to drop down to 500 may be even 450 i.only weigh 13 stone
lol you done the spring calculator on tf tuned?
http://www.tftunedshox.com/info/spring_calculator.aspx
i weigh less than 11 stone lol, but my bike isnt single pivot and only has a 2.5" stroke shock, so a 350 is a very light spring.
i reckon you should try a 400 mate
initially things feel way too soft, but ride it for a bit, as long as you aint a clumsy rider, you should feel the benfit!