OM, after talking it over and revisiting the studies I could find, it looks like diluting alcohol for cleaning a wound has negligible effect. The most important overall factor, it seems, isn't what you use to clean a wound, but how much pressure you use to irrigate it. Just pouring any liquid is going to be less effective than using some pressure. The PI solution is recommended when potable water is in short supply.

Even when water is in short supply, using good technique doesn't use a lot of water. As little as 100mL can be effective (although this depends on the size and level of contamination of the wound).

Hope this helps, and that it's information you never have to use!