I'm aware that F17T8s can be used on F20 preheat ballasts safely (and will even make the ballast run cooler), but does this apply to F32T8s on 2x40 HPF preheat ballasts also? It seems like higher arc voltage would mean lower arc current and thus less stress on the ballast, but does the capacitor change that? I tried a pair of F32T8s briefly in one of my 2x40 preheat fixtures and they worked fine with certain starters and blinked continuously with others. Obviously they were overdriven, but F32T8s seem to be able to handle operation at above full power reasonably well.

Probably need to check the ballast with one of those infrared devices that can observe the temperature of the ballast.

F32T8 isn't a retrofit for F40T12. Operating the american energy saver T8 on T12 ballasts can reduce the lamp life.

Has anyone experienced F17T8s reaching EOL faster on 20W preheat ballasts than on the electronic ballasts they're designed for?

Dor, it makes them brighter. I did manage to get some 36 watt European T8 lamps. NO, they won't even glow a little on rapid start, but work fine in my 1950 something preheater. I can get F32T8 to run on good high power factor rapid start, but they are really overdriven.  As for shorter life for a F17T8 on preheat, most likely so just being preheat.

It seems like higher arc voltage would mean lower arc current and thus less stress on the ballast [...]

Only on LPF ballasts. HPF ballasts are able to maintain current over a very wide range of arc voltage, so in the case of HPF ballasts, the higher the arc voltage above rated, the more stressed the ballast will be. Put simply, I'd never do it for anything more than a quick test. The starter situation would be because the arc voltage is high enough to trigger some starters. Electronic starters should work fine, though. And there may be a European-market starter that would work better.

As for LPF ballasts, knock yourself out. In fact, some residential grade ballasts like the Advance L-140F-TP actually run the F32T8 at rated current.

And there may be a European-market starter that would work better.

I don't think so, as all European lamps for the preheat cicuit have the arc voltage below ~110V (correspond to the F40T12; about the maximum for the 230V OCV provided by the series choke ballast), so starters for such high arc voltage are not necessary here.
I would rather expect such starters to be available in the US, where the step up transformer is necessary anyway (so the OCV may be way higher).
So if starters for 140V (or above) lamps are not made for the US market, I don't think they would be made anywhere else...

And for the electronic, you need the types with "EOL cutout" protection (so e.g. like the Philips S10e or similar).

the F17T8s that run on preheat on the magazine racks at walgreens have been out lasting the F18T8 lamps, I actually have not changed an F17T8 in preheat yet! but the ones that have cheapo electronic RS ballasts seem to eat lamps regardless
the F17T8 lamps in 1 lamp trigger start at EOL just do a dim flicker

Some of the NPF or LPF are designed for 32 watt circlines and will also run f32t8s. I have tried this on an universal 202-B-TC-P ballast and the ballast runs quiet as a whisper and only barely heats up.

Some of the NPF or LPF are designed for 32 watt circlines and will also run f32t8s. I have tried this on an universal 202-B-TC-P ballast and the ballast runs quiet as a whisper and only barely heats up.

But really just the NPF, the HPF may overheat in the same way as the F40 ballasts. The 32W circline is 0.37A/95V.

I just wouldn't use them on old delicate lead lag ballasts though.