One thing to note is that the implementation language matters significantly less than the method of handling database accesses. According to the sh.itjust.works admin team who announced an upcoming migration from Lemmy to PieFed this year, Lemmy's handing (which used to be fairly crappy, requiring routine machine reboots rather than solving the issue of leakages) has recently gotten much better.

Another reason PieFed performs so well is that it is 25-fold more efficient in pulling data from its servers than Lemmy. That is a design choice that hopefully one day Lemmy will catch up to making also.

Thus, the choice of back-end language - Rust vs. Python - is much less relevant than all of the other factors involved. Although it does result in very noticeable downstream effects, particularly the increased speed of adding new features.

I would even go so far as to say that the choice of software itself - PieFed vs. Lemmy, or Mbin, nodeBB, Mastodon integration, even mostly-dead (though reportedly undergoing revival!!) projects like Sublinks - works out to offer far less of an impact to your overall experience than the choice of admin team. e.g. the .world and .zip teams both offer both Lemmy and PieFed options, and if you use something like Voyager (which only offers "experimental" support for PieFed), then you will barely notice the difference.

Your other questions are answered already but I hope this additional information has been of interest as well.

Edit: another consideration is whether you want to host your own instance. For that I would unhesitatingly recommend PieFed as by far the easiest to deploy (especially via the docker container) and using least resources. Tbf, that is not from 1st-hand experience but so very many reports of others do state this.