> I haven't picked my LED's yet, but I know their Vf will be less
> than 3V

Just when you thought it was safe to go back in the water ......

If you use PWM to drive the LEDs you may not need current-
limiting resistors. Adjust the duty cycle to suit the supply voltage

Up till now you've been talking about driving the LEDs with static
or standing current. But LEDs have another parameter - peak
repetitive current. This is in the order of a few amps for short
pulses. What mostly kills an LED is watts. Too much V or too
much I. By keeping W in spec you can take liberties with drive

Two examples -

Infra-red remote controls. To get distance, the IR LEDs are pulsed
with high current. In the schematics shown below, 500mA. Current
as DC that would fry them

http://home.clear.net.nz/pages/joecolquitt/txless.html

Moving signs. The LEDs in commercial units are strobed on a 12V
or more power rail, and may have as little as a few 10's of ohms and
draw significant current for short periods

The trick is speed and persistence of vision

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