Hello,
Overclocking the CPU doesn't improve FPS drastically. Most of the people overclock their CPUs over 1GHz just to get around 6fps.
Since you are running the game on 900p there won't be a big performance hit. But I don't think you can play with high settings with stable fps. I am being very cautious around this assumption.
If you run on 900p and use normal settings it would hit around 50fps. But make sure you turn settings like "Grass Quality" to low.
Hope this helped