Oh man, I so envy you on that 5500!!
Never had a V5 before ... or Voodoo4 even. The most powerful Voodoo in my entire collection is V3 3500 which might even work OK, but it's never been tested due to the fact it's missing that blue AV splitter cable thingy (and the actual card doesn't have VGA output), so I can't hook it up.
As for the memory upgrade feature, yeah I have couple of those actually... Including this Rage Pro card, which is now used for one of the systems but I don't remember which one.
Edit
Oh wait, nevermind... I know which ones you were referring to! Rage indeed has the memory upgrade thingy, but this one is newer. You probably meant the older style, with individual sockets for each EDO module?