Yes it's worth it to spend $20 more on a 4770 than a 9800GT, but both loose to the 4850. The only reason to choose the 4770 over the 4850 is if you have a weak power supply or can't deal with the extra heat.
Anyway if you're just comparing the 4770 to the 9800GT, the 4770 is just below the level of a 9800GTX/GTX+ so it's considerably faster, but if you're just playing the SIMS or something, or game at a low resolution like 800x600, then that doesn't matter :lol:.