Well I have many experiences with Syrian Rue and cactus together...in fact I think that pretty much all of my prior cactus experiences were combined with Syrian Rue...and I have one experience with mesc extract and rue.
I know the MAOI + mescaline gets bad press in some circles...but it was always good to me. My feeling, based on my experiences, is that, unlike a mushroom or DMT trip, the character of the Rue exerts little of its own character on the cactus experience, perhaps due to it's phenethylamine as oppose to tryptamine nature.
However, it allows one to eat 2-2.5 times less cactus for an equivilant dose...this allows one to go really deep with the cactus, and I've had some very deep, extra dimensional visionary experiences with this combination. Adds a bit more time on to the trip though, and you will very likely purge, possibly several times...don't fight it. Very euphoric body bliss.
A while ago now myself and a fellow explorer ate some 10x Syrian Rue extract...was tarry and a bit weird..never touched it again...but it made my friend repeatedly purge over, and over again, and really knackered him.
So with cactus, a little Rue goes a long way, no more than 2g I think...above this there will be very little increase in MAOI activity, but possible increase in unpleasant side effects.
I had one experience with Rue and a low dose of xylene mesc extract from San Pedro...I didn't like it actually. Increased the body load, felt just a tad unsteady on my feet, my stomach was weird for a long time, and felt 'dirty' for a mesc trip...so I won't be doing that again. Now THH + mesc, well that's a different story...