The fact that you see the SGS lag in YouTube has NOTHING to do with the CPU. Samsung chose their RFS for a filesystem and it causes the IO lags. I had exactly the same lag until installing the app "one click lag fix" which sent my benchmarks through the roof and made it easily perform like the LG (testing here on wireless it wins).
I know "it's not stock" and "you can probably optimize the LG as well" but the Galaxy S has a LOT of optimization potential due to poor choice of file system. I've not seen another phone as of yet that has that much potential to unlock by making some very simple modifications.
And the SGS GPU is still king.
Having said that, it is funny to see how a horribly lagging SGS is still much faster than iPhone 4 :) No flame intended, let's not get our fanboy on.