Why don't the N64 Zelda games look like 20fps to me? They seem really smooth in general. A framerate like that would kill just about any other game for me but I can't really notice it there (I do notice the drops from 20, but they aren't even that bad).
Anyway performance is a big deal when talking aobut N64 games so taking that into account I'd say Majora's Mask and Banjo-Kazooie balanced their visual to performance ratio best. Conker is unrivaled at its best but there are some performance issues that can get annoying particularly because platforming/shooting are hurt by poor performance more. DK64 is just under Conker.
Banjo-Tooie and Perfect Dark (single player) sacrificed too much performance I think. Perfect Dark multiplayer doesn't seem as bad.
I'd include Indiana Jones and the Infernal Machine if it wasn't such a glitchy mess. It looks really good with the expansion pack(480i I think) and the performance is alright for the kind of game it is. A lot of visual glitches (like large areas flickering) or other strange issues (like swimming in the air) though.
Just my observations. I don't know the actual numbers but I've tried all of these on original hardware within the last six months.
It was revealed in the Conker's BFD
directors commentary that the only reason DK64 required an expansion was because of a random bug in the 4MB version that would crash the game. The expansion 'fixed' it, so they had to lose money and ship it with one.
I think this comment was misunderstood.
I got the impression that there were two "builds" of the game. One that didn't utilize the expansion pack and one that did (for extra effects). These would have, of course, shipped on the same cart and would have been a simple menu toggle. The 4mb (default, non-expansion) build had a bug that Rare couldn't track down and fix despite their effort. This left them with only the expansion pack build as stable so it became default.
I'm sure the DK64 we got still needs the expansion pack.