Does connecting 4 LEDs in parallel use more current then connecting 2 in series if the resistance is high enough?
Assuming you set your goal to drive the LEDs at their minimal (optimal) currents i1 > i2 > i3 > i4, your initial (a) design will dissipate power as:


  Pa = U × i1 + U × i3 = U (i1 + i3)


(Each branch driven at the highest current of the LED pair since shining brighter is OK, but dimmer isn't)

Your secondary (b) design goes as follows:


  Pb = U × i1 + U × i2 + U × i3 + U × i4 = U (i1 + i2 + i3 + i4)


From that it's easy to see that the initial design is more efficient.

But...

Seeing that your supply voltage is 3.3 V, you should watch for the combined voltage drop of the LEDs. By having two LEDs in series you add up 2 * Vled which, if close to the supply voltage, leaves little margin (if any) for regulating the current through a resistor.

It's also useful to know that, leaving a small voltage drop across the limiting resistor calls for a small valued resistor. The consequence is that your circuit gets more sensitive to small fluctuations of the supply voltage and also depends more on non linearities of the LEDs themselves.