Once you ballast over the foam pretty much all with give similar results noise wise. The best noise cancellation I've seem came from using gauge master/noch ballasted foam rolls. This is basically foam roll pre ballasted with noch granite made to fit standard track. You slot it into the track and glue it down. Noise reduction is nearly 100% and it looks like perfectly ballasted track. You can then get bags of matching ballast to go between lines.
http://www.gaugemaster.com/item_details.asp?code=GM200
http://www.shapeways.com/model/89699/cie-2-axle-timber-wagon-oo-scale.html?li=search-results&materialId=6
Is another option for the 20' version. I've a few of these and they are good too.