A bit of a wierd question, but maybe there is a guide somewhere on how to enable 3dfx support in the gog version of vanilla Blood for dummies? I saw mentions of some 3dfx patch for the disc version, is it worth patching the game or is this patch already included?

The 3Dfx patch is an odd one. It was released as an upgrade for Blood 1.11, resulting in Blood 1.20, OUWB is 1.21, but has none of the 3Dfx enhancements.

RTCM has a OUWB-3Dfx patch for Blood 1.21, that you could try, I've never really bothered with it though:
http://dukertcm.com/knowledge-base/downloads-rtcm/blood-patchs/

Thanks for the link, a quick search only brought up old forum posts with dead links. I'm just curious to try out the dosbox-x/dosbox-stagning emulation, but I don't think I have many games with 3dfx support in my library.