I don't think you will have any problem using the FZT705. Its switching speed is up to the task. The only penalty that you will pay for the use of a darlington device in place of a non-darlington device is the Vce saturation voltage for the darlington device is just under a volt for the small amount of collector current that the device will be switching. Your output will swing between +4V and 0V which should be adequate for the CMOS input you are driving. Vce saturation for the non-darlington device is more like 0.2V which would give you a output high level very close to the +5V power rail.
Just something to keep in mind as you go forward with you project.
Good Luck,
hgmjr
Just something to keep in mind as you go forward with you project.
Good Luck,
hgmjr