SVG Filter - results pixellated?

I'm trying to create an SVG filter that works very well in Inkscape, but so far no luck in Ai.

The Inkscape filter is found in Filters > ABCs > Roughen, and basically uses feTurbulence and feDisplacementMap to create a very nice wiggly line that IMO is more realistic than Illustrator's "Roughen" filter.

Original path:

After Roughen:

In the Inkscape file, the filter looks like this (with the filter renamed to myRoughen):

<filter

    color-interpolation-filters="sRGB"

       id="myRoughen">

      <feTurbulence

         result="result91"

         baseFrequency="0.04"

         type="turbulence"

         seed="0"

         numOctaves="3"

         id="feTurbulence3810" />

      <feDisplacementMap

         in2="result91"

         scale="6.6"

         xChannelSelector="R"

         yChannelSelector="G"

         in="SourceGraphic"

         id="feDisplacementMap3812" />

    </filter>

Saving this file as plain SVG and importing into Illustrator, the path is there, but the filter comes out pixellated:

Zooming in on the pixellation:

Looking at how the filter got imported into Illustrator (ie, going into the Edit SVG Filter window), we see:

<filter  id="myRoughen" color-interpolation-filters="sRGB">

        <feTurbulence  result="result91" id="feTurbulence3810" type="turbulence" stitchTiles="noStitch" numOctaves="3" baseFrequency="0.04" seed="0">

        </feTurbulence>

        <feDisplacementMap  scale="6.6" in="SourceGraphic" in2="result91" id="feDisplacementMap3812" xChannelSelector="R" yChannelSelector="G">

        </feDisplacementMap>

</filter>

which seems pretty much what it should be. So what could be causing the pixellation? As far as I can tell, there's no dpi setting associated with saving the plain SVG file from Inkscape, or with displaying the results of feTurbulence in Illustrator.

On a lark, I wondered if increasing the size of the line in Illustrator would help. Nope. All I get is a thicker pixellated line:

Any help?

Thanks

Tom