When building the kits for xmas I looked at alot of these and came to similiar conclusions. Here are some of the things I found:

lifestraw specifications:
http://www.lifestraw.com/en/low/specs_low.asp

lifestraw test results:
http://www.lifestraw.com/en/low/test_results_low.asp

Good info here:
giardiaclub.com

Extremely good resource, found by accident on google.. read at your own risk:
http://usachppm.apgea.army.mil/WPD/PDFDocs/FinalReport.pdf
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