Well, with my romset, we've already got plugins that work well and are fast enough for a GHz Pandora at least. Only DK64 still has a slightly screwy camera IIRC, and Mario Tennis only works slowly under the oldest plugin, and even then the character models are missing (you have to try to play using their shadows!).
The GlideN64 plugin is very promising. It tends to run most things at about half speed on my system at the stock 1GHz, to my eye, which is better than the old GLES2 plugin, but it also plays a better game of Mario Tennis than any other plugin.
However, it does pause during shots, and while it's paused it's absolutely thrashing both my OS card and my appdata/roms card. I've no idea what it's doing, but I'd imagine it'd be intolerable for anyone with slow SD cards. As is, I managed to win my first set in Mario Tennis, under emulation. It got stuck in a loop at the start of the next set that lasted over 10 minutes, after which point I killed it, but that's the best yet. It got a few effects wrong, such as the shadows being rendered in the top left corner (I think that's common with other plugins too, as that mess in the corner looks familiar, although those stall before the game proper starts.
Unfortunately, it looks like I didn't rip Perfect Dark, and my carts are in storage at the moment, so I'll need to fetch them out and hope I've not lost the cart.
I gave it a quick run until my left nub decided to screw itself up. MarioKart runs well with the Rice plugin, Wipeout64 too (although I got a freeze which I killed with a long hold of the Pandora button during the first challenge race), Lode Runner I couldn't navigate the menus properly, but I was probably running the wrong video plugin while testing that.
I'll have to give this a better test, but I'm currently in the middle of listening to a podcast so don't want to reboot. I'll try to get through that in the next couple of days then test further.
Okay, done a bit more of a full test using the Rice plugin exclusively. Last time I think I was running the ES1 version.
Paper Mario has introduced a flicker on most screens up to the second save point at least. REGRESSION
Mario Tennis ran well - bit of slowdown, and the shadows were all tucked up in the top left corner, but it's the first time I've been able to play a game successfully on my Pandora. IMPROVEMENT
MarioKart ran flawlessly again
Killer Instinct Gold continued to run well.
ISS98 still plays with messed up text.
International Track and Field 2000 didn't start (but I don't ever remember playing that on my Pandora, so I think that's unchanged)
FZero wouldn't start. REGRESSION
Donkey Kong 64 ran well apart from the existing camera glitch
Overall, while Mario Tennis is nice to have, based on the Rice plugin at least, it breaks more than it fixes.
Trying out some other plugins on those problem games, Glide64 makes the window furniture and text disappear from F-Zero, which makes it hard to work out whether you've won. On the other hand, Arachnoid makes the furniture appear, but doesn't render the track properly, which just makes it hard to win!
On Paper Mario, most of the other plugins make it flicker even more, but Arachnoid is arguably better than Rice, keeping steady for seconds at the time, but at other times making text completely unreadable by disappearing the text after half a second of reading it.