What a funny thread this turned out to be. On the one hand, a bunch of Dutch speakers, who (only) seem to relish having "found" each other, with the idea of starting up a Dutch-only game; then on the other hand, a flock of "Anglo's" who have some connection or other with Holland and who immediately start hair-splitting on which Germanich language might be how few percentage points closer to the other germanic language, something we Dutch NEVER ever even think, let alone discuss, about.
Like: Who cares!! All our (Dutch, Danish, Norwegian, Swedish, Icelandic, German, English) languages are Germanic; how Germanic, and how closely they might, or might not, resemble each other is truly a moot (I think the word moot must have been invented for this point) point....
But now that we are into it, perhaps suffice it to say that I as a native Dutch-speaker (assuming I had had no foreign language training and skills - which is a giant leap of phantasy) believe that I would have understood about 65% of a discussion with an equally monolinguistic German, but only about 10 % in the case of meeting up with his Danish equivalent (or Swedish, or Finnish, or Icelandic). If a mono-linguistic Dutchman (i.e. in this case having no English skills, of which there still exist a few here and there, mostly the unedicated very elderly) would meet a mono-linguistic English speaker (of which there are of course zillions) I believe he/she would only be able to understand also about 10% of the other, and perhaps equally vice versa.
Upstart of this: From a Dutch-speakers point of view, German is by far the most closely related, and possibly this also applies the other way around.
Hence the (reprehensible!) idea of many Germans that Dutch is simply another German dialect..... (although in truth, that view is objectively speaking easily understood and when we are really honest, as Dutch speakers, there is an essence of truth in it).