I completely agree with the above
Though I can identify to some extent with many of the issues in this thread, I mainly feel the need to rant about performance.
WHY DOES IT RUN SO GODDAMN SLOW EVEN ON A QUITE GOOD PC AAAAARGH
On the difficulty level thing, I sort of agree with Brichals BUT on the basis - as you mentioned - of using house rules. Specifically: 1) never sign RAs, as well as it being unbalanced the whole way it works just annoys me, and 2) never sell irrelevant open borders to the AI for cash, exploity and stupid.
On that basis, I play prince/monarch on Civ 4 BtS and king/emperor on Civ 5 so Brichals' 1 level thing holds true for me. The difference of course is I need house rules to enjoy Civ 5. Without them I have actually won one Civ 5 game on Deity but it was a tedious grind and I have no wish to ever do it again. Whereas in BtS I am quite happy to abuse, for example, Slavery as much as I can because it makes sense to me (as a gameplay mechanic) and the AI can also get at least some use out of it, so fair enough.
EDIT: hmm yeah actually been playing BtS + BUG/BetterAI so long I forgot BBAI is at least 1 maybe 2 levels higher than standard BtS, so yeah maybe there is a bit more than 1 level difference between Civ 5 and standard BtS. But definitely not Emperor = Chieftain or whatever was originally claimed, that is an exaggeration.