PS Watercolour effect on large print

[clive_temple]

Hi,

I was playing with the effect on a small, low dpi photo.
http://www.pbase.com/clive_temple/image/69867808

But now I want to apply it to a large, high dpi photo but it doesn't have much of an effect, could anyone please suggest how I can get a similar effect to the above photo on a 900 x 600 mm, 300 dpi photo?

Thanks in advance.