For what it's worth I've done many km's with my DNA filter and DNA filter cover on dust filled roads behind other riders and never noticed any spec of dust past the filter. If you use the filter with the original snorkel cover, it apparently doesn't seal against the DNA filter and you will get lots of dust past the top of the filter.
Personally I think your easiest power gain on a Tenere is to fit the DNA filter, the stage 2 cover and the Kev's O2 and fuel mod.

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2014 XT660Z - Barrett pipe, DNA stage1.5, Barkbuster hand guards and handlebars, Pivot pegs, Teknik suspension, Guard-it engine protector combo, B&B rear rack, Trax topbox.