Really useful thread and link to Jim's (always detailed and well-explained) post good to read.
Ive found that adapted lenses (for me MF nikkors, Leica R, Zuikos some canon FDs) to a range of full frame cameras (mainly EOS, Sony) have been very affected (from mild to quite detrimental) by the adaptors, including the expensive ones. The inconsistencies have been great: both the adaptor (variation from e.g. one novaflex to another etc) and also the sensitivity of the lens to its registration length due to the internal focusing designs etc. Central focus has been fine but edge abberations often high. Wide angle primes and wide zooms seem most susceptible.Other lenses very immune (eg Leica 280 F4 Apo Telyt).
Ironically buying cheaper adaptors and experimenting to find one that works well with a particular lens seems anecdotally better than hoping that lots of $ spent on a single adaptor might see you right. Or buying second hand and trying several to find "the one". Compared with the manufacture of lenses (mechanics and multi-element optics) adaptors seem to be in company with filters: expensive for what they are and often very poor/purposefully lax QC.