Thank you for all the nice replys.
I have gwx3 with SH3 already. I never even tried it without so i can't really say how it improves it cause i never saw the stock one. But i must say i like it so it must be good.
The reason i am asking about SH4 is that i am a poor student and don't have that much money to spend on games and i was thinking it's useless to buy it if i just play it couple of times before leaving it for SH3. It's not that pricey anymore i see but one gets lots of food with that money anyway.