It wasnt a bad idea imo.

with my spellspeed my global is about 2.23 seconds. It shaves off the bliz 3 cast (global 2.23 seconds) but it adds casting time to the fire 3 (3.12 seconds as opposed to the minimum 2.23). This is a net gain of 1.34 seconds. So my rotation cycles through 1.34 seconds -quicker-.

the problem: also simply tested with my current spell speed, unless server ticks are VERY favorable (like 1 in 10) then i'll get 2 mana ticks, I need 3 at ice 1. This means while I saved 1.34 seconds, I cost myself 1 fire IV from my next cycle. This is a loss.

His idea may work for low levels of spellspeed.