I tried it for a bit but I do way better with GP, says hotslogs. So, while I'd like to have it... its for your longest CD basic spell and only makes you profit in certain situations, while GP always ups your damage, which is, after all, the most important thing. You doing the damage deeps.
Going for GP you obviously never can tell how hard it's gonna be to keep those stacks going, but there's still the at least 5% extra I guess (compared to, again, the effet on E which might not help yout AT ALL in certain situations). It of course also helps that I'm mostly doing a good job at not dieing too often with him.
Might be a bit different in Soloqueue of course (how would I know!
).