It is significantly faster. The green cards are underclocked a bit from normal 9800GT speeds but not nearly enough to make up the performance difference. Also you can easily put the 9800GT back up to normal speeds(and beyond) with an overclock.
The two cards that you have mentioned are old now so going for them will be an mistake when dx 11 are everywhere in the market....
So specify your budget and if you already have buy either of the card then the answer is 9800gt is more fast than 9600gt as everyone have already posted.
I have already bought the 9800GT Green. I was wondering if 9600GT was better and that was why I was asking. I have Intel Pentium 2.4ghz core 2 duo, Nv idia 8600GT (will upgrade to 9800GT), 2GB ram, 250GB HDD, PSU Gigabyte 460W. My monitor is 19 inches. Thank You all for the help!
IF you have already bought the 9800GT Green then don't worry it's way better than the 9600gt and you have made a good choice of choosing the 9800GT...it's a great card will be fine for your purposes.
Thank You very much! I was really wondering if I made the right choice and now atleast I know I did. I ordered the 9800GT but I got the 9800GT Green instead and I thought that it will be much slower but I am happy it isn't.