Of course in all cases there is a dependence on actual current levels, but as I remember it "back in the day," the nominal forward drop of typical germanium devices was 0.3 volts and silicon, 0.7. The big deal about Schottky devices was they had the better temperature range and lower reverse leakage typical of silicon devices combined with a lower forward voltage. A few tenths of a volt difference in a device carrying -- say -- 20 amps -- is quite a difference in power dissipation.
There is quite
a detailed document on the Butkus site about some of the substitutions and conversions to replace mercury cells. EDIT: Already linked way back. Note it does not say a 1n4148 is a Schottky, it is a straight silicon switching diode (a classic, actually) and is saying it can be used to replace TWO Schottky diodes in a two cell circuit; it's all about the voltage drop.
Back when, I tried a CRIS adapter in my Gossen Super Pilot, but found the battery holder arrangement in the meter was a sort of mechanically sketchy affair that couldn't hold the adapter solidly enough to maintain reliable electrical contact. So I opened the meter and put a diode in. Don't know if it was the diode, or just "how it was," but the sucker was a total slug to come to a reading. I vaguely recall it was always slow, but had not used it in years, as my later cameras had built-in meters. So after some contemplation, I bought a Digisix -- and in a later GAS attack, a Sekonic L508! Problem solved -- throw money at it!