Hi Etienne,
I'm going to try to answer your question - all is strictly "in my humble opinion" of course! :)
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I am looking for a not-collectible, not pristine HP-48, as a "discovery machine" for this generation of calculators. [Is RPL that evil? :-)].
I think they're great machines. I have never shared the "negative feelings" about the 48 series' complexity or unfriendliness, and I've always loved RPL - to the point that I just "put up" with RPN because I can't get RPL on a smaller machine! ;)
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The Gs are naturally more expensive, and I wonder if you could share your experiences with either/both series.
If you find a well-used one (see my recent post) the price difference isn't much. It all depends on the condition and on the seller's choices, but a good GX can be had for less than many sellers ask for a S/SX.
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- is one series sturdier than the other? (they seem difficult to open/refurbish/repair)
They *are* very difficult to open. It can be done, and I've done it several times, but especially the first time it's difficult to end up with a machine that looks (and especially feels) like new. And it's time consuming.
Apart from that, as far as I can tell the build quality is exactly the same (though the later Gs, made in Indonesia, have painted keys instead of molded).
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- are 32k RAM useable, or should I target a 128k machine (SX+extRAM or G+ or GX), or should I expect to need even more?
32KB are not much. I started out with a G, and I found myself constantly moving things between the computer and the calculator. And most downloadable libraries (i.e. the wonderful speedui) simply *need* 128KB. So I'd say go for a GX, even though you'll probably never use the cards.
If you buy a G, it's rather easy to replace its memory chip with a 128KB chip, turning it into a GX without the expansion ports, but again, you'd have to open it and you have to be good with a soldering iron.
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- are the S- "fast enough", given the "typical" problem you throw at them?
I honestly find the S series too slow. Not just in programs or complex calculations: all the UI is much much slower and unresponsive. And the G/GX also have added features and commands. I'd say, if you're not going to collect but use it, go for the G series.
So all in all, I'd just find a good, non-pristine GX or an expanded G if you can find it.
Hope that helps,
Cristian