4N35 level optos are pretty bad, you wouldn't want to use them above 100kbps or so without
special hardware. (Hmm, I have the schematic of the circuit I was referring to, but it doesn't look like I posted it there.)
For doing better on the cheap, I would go with 6N136, or the high dV/dt equivalent SFH6345 (be warned, the dV/dt rating on 6N136s is
very misleading). They're good to 1Mbps easily.
Both of these, you just add a pull-up to the open collector output. Or the 4N35 can be wired "emitter follower" style (though it's not actually following anything), in case you need the diode end in a particular direction and you need the inverted (or not) output. (You can't invert a 6N136 output in the same way without defeating the high speed feature.)
For more, I'd go with logic level parts, or iCoupler style devices. There may also be power advantages, say, if you need to be miserly with battery power (a logic level opto probably uses less bias on the output side).
If you need to be really miserly, you might resort to building your own (say with planar coils and RF design). But, geez...
Tim