Ski speed is determined by ski camber profile, ski base structure, and wax choice, in that order. For kick wax, a really good camber profile makes getting good grip AND glide much easier.
I don't have recent experience with Holmenkol, but I can say that Toko, Swix, Start, and Rode are all fast in the right conditions. There are definitely days where one brand is faster than the others, but it isn't the same brand every day.
If you ski in cold, dry conditions, add Start green glider to your box. It is cheap and very fast for very dry, fresh snow at -8C and colder.
My personal feeling is that for the LF waxes, Toko is faster than Swix for high humidity and Toko is slower for low humidity.
If you have the money, the time, and lots of skis, you can buy all the brands and test ten gliders and ten grip waxes each race day. If you can hire a personal technician, even better.
I glide wax two pairs of skis the night before, and race on the pair that tests faster. For classic, I test grip wax on the slow pair and put the final choice on the fast pair.
I train on Toko LF gliders, as they seem to give the best price/wax wear performance on my local snow.
I agree with Glenn G: pick a brand and get to know it.