I have as well peyote as san-pedro (pachanoi), growing in my house.
I'm wondering if both cactusses would work synergistically together. For both i have enough for one strong dose; the san-pedro is about 40 centimeters long (that's about 17 inch) and the three peyote's are in size somewhere in between a golfbal and a tennisball.
The question is: would i take the whole sanpedro at once and the peyote's some other time, or would i take half the sanpedro with half the peyote's each time?

I can not tell you what to do, but I can reassure you that there's no problem in combining different cactuses. They all (T. pachanoi, peruvinaus, bridgeesi, L. williamsi, etc) contain mescaline in different amounts, so at the correct dose the combination would be almost indistinguishable from a mono cacti trip. Almost, there are some slightly psychoactive alkaloids that differ between the species, but this is not a problem. It's at least not something I've heard of. I would say you can combine them however you like, just focus on the dosage (whereas I always recommend extracting to be certain)!
Have you used mescaline before?

I have used both san-pedro and peyote before. But the san-pedro i used before was a peruvianus, it was pretty weak. And with peyote i have never taken large amounts.

I have never had a visionary mescaline trip. The effects of mescaline i am familiar with are the 'XTC-feeling' and visual effects like seeing aura's,'stroboscope-effects' and some other simmilar things.
So to me, till this moment, mescaline is a sort of XTC with interesting visual effects and it never had the depth to me of ayahuasca, DMT, mushrooms or even LSD.

I know from sources that include posts on this forum, that it can give psychedelic breakthrough experiences. So i'm gonna try larger amounts as soon as possible.

But besides mescaline, they also contain other alkaloïds. if there is a synergy between those alkaloïds, then peyote could realy add something to the sanpedro.

^^Its hard to judge whether or not they would synergize or add on new effects. Often with plants and mixtures there are differences then with pure compounds but its often hard to tease apart subtle subjective effects versus obvious differences between active components.