Well it's probably just something like no matter what you take when you're combining the MAOI and DMT then you'll still be trippin, but with possible qualitative differences.
I understand your question and I cannot answer it. Of all the reports out there that I've read there is quite a few individuals who feel the energies from the plants. Rue being typically more masculine and caapi typically being more feminine.
These weird little energy variances could very much change based on the effect you so desire.
When I'm smoking MJ I typically enjoy a sativa during the day and a heavy indica stone towards the end of the night (the kind of indica stone that makes my contacts dry out, so I actually have to take them out) Just saying these qualitative differences are the basis of which specific bag I'll choose as in the OPs ordering harmala source question.
When I'm with my boys all day I'd like to make the moment for my lady at night. Maybe rue would qualitatively be better for day tripping while caapi for night, respectively.
I definitely see a variance in species or even location changing the total chemistry of the plant. If you are so accustomed to these plants that you are sensitive to these fluctuations then you may answer this very question as it comes. So with no experience and assuming you don't get a better answer, try try again
You have your whole life ahead of you so even if you didn't have the expenses for a year theres still later. Rue is cheap, I'd say get that and then save money to try caapi. or better yet, source what you have from around you if possible (I don't want to extract from reed canary grass no mo!)
I say the experiences of not really knowing for sure and finding out for your self is probably the most exciting and self-fulfilling paths you could take!