Using tick volume turns out to be a decent representation of forex volume, so I'm wondering what people think about the historical volume from histdata.com I actually cannot find volume I can pay for... It seems to all be free, which is worrying, a little. http://www.histdata.com/download-free-forex-data/?/ascii/tick-data-quotes
Using tick volume is not a decent representation of volume. It just shows you how many requotes are occurring. With knowledge of the source of data, I don't think it's worthwhile to use it. They could completely change sources from day-to-day and you'd be trying to infer relationships that aren't there. Can't beat the price, but the provenance is questionable.
Do you have access to CLS? I can't get it. There was a study I read about which showed a 90% correlation between tick volume and real volume. Let's say that is now decayed to 80%. That's still decent! Futures volume is difficult to map well as finding volume for expired contracts is a pain. But I also did look into this and may run a study at some point to see their correlation.