I doubt you see much difference in offset ku lnbs, no matter what you do unless matched commercial parts are used.

Changing from a dro oscillator to a pll oscillator does not help performance unless additional circuits are added. Even then, only under certain conditions will a well built pll help.

The trick to better performance from a good or decent small offset dish is to find a lnb that is a good match for it, so it is a bit of trial and error.

Make sure the lnb is positioned on the dish as it was designed to be, and pay close attention to dish adjustment and alignment. These two things will probably make the most difference in received signal strength, provided a decent, healthy lnb is being used. Need more signal? Get a bigger or better dish. The lnb can only be as good as the reflector it is mounted on.