the cards are in the same tier, although the 4890 has slightly more raw power. But you have a GTS450, which is only one tier lower. I would definitely recommend staying with the same card or going higher as you're getting a relatively small increase in performance for going with a 4890 over the GTS450.
Probably a 6970 for ~170 is where I'd start if I were to upgrade from where you are. If you've never read the tom's hardware best graphics cards for the money, they're a great read.
The 4890 is faster than the 5770. 5770 about a bit faster than the 4870. Whats your native resolution?
Other factors also comes in as the 4xx series cards eat more power and run a bit hotter with more noise and no Dx 11 support
The 4890 is not enough of a step up over you current card.
Save a few more bucks and aim a little higher, or you are going to feel like you just blew $100 for a useless upgrade.
Rule of thumb, you want to jump at least full 2 tiers when you upgrade a GPU or you won't see a very big difference or feel like the money you spent was worth it.
I am going to buy XFX HD4890 XXX EDition it costs me approx $100.. No Pakage contents ONLY CARD.
Do you guys recommand me to buy or is this card worth for new games ?
Currently I have Installed GTS450, should I replace with that or HD4890 is good for today's generation games?
Radeon 4890, Radeon 5770 are of similar performance now because the drivers are fully matured for Radeon 5000 series and Radeon 5770 has the advantage of being highly power efficient and Dx11 support as well. A geforce GTS450 is equivalent to a Radeon 5750 at max..........