[popcornmix]

are you sure? I get a pll of 1220 with core @ 610, unless I'm reading the formulae wrong?

Ah yes, if you add max_pll_freq=2440 to config.txt what I said would be true..

That means:

If you set core_freq=610, yes you will get a pll=1220.
If gpu_freq is not specified will aim for 250MHz using the largest even divisor of pllfreq.
In this case you will get 152.5MHz which is a bit low.

So in this case, you should specify gpu_freq=305 which would probably work okay.

Or, avoid_pwm_pll=1 would use a second PLL for gpu, which means you would get exactly 250MHz (but analogue audio may be degraded).