Tuning of a cheap opto coupler (for gate driving/level shifting)

[mrx23]

Here is a schematic that can multiply your optos bandwidth. (for example ClassD gate isolation/leves shifting)

You sould take the output signal from the collector and the base and left open the emitter.

One disadvantage is that you can take out smaller current, but an optocoupler is not for amplifing

http://www1.jaycar.com.au/images_uploaded/optocoup.pdf fig 6a

http://onlany23.atw.hu/opto-couplers.pdf fig 9

I want to use this in isolating a 250Khz TTL PWM signal which goes to the MOSFET gate driver.
(The driver needs only 1uA current input)
I need a rise/fall time of max 100nS.

And I want this rise/fall time with a cheap 4N25-4N35
(which has 2000ns r/f time in standard collector-emitter connection)

Dose anyone tested this faster use of an opto coupler?
And mesured the rise/fall time?

I know it would be simplier to use 6N137 or faster optos,
but I cant get those in my country (and for cheap).