1: You want to make sure your PSU has enough wattage and amps to be able to handle either 2x 4770's or a single 4890. You also want to make sure the PSU has enough connectors.
2: You need to make sure your MoBo supports dual GPU's (crossfire) and also take into consideration if the PCI slot will run 2x16 or some other variant that may be slower, like 2x8.
3: You could also consider waiting for the newer gen GPU's to come out for DX11 support. If you have a "decent" gpu now, i would just wait. If you don't want to wait but are interested in upgrading later (in a few months when the dx11 cards do some out) you could consider a 4850 to tide you over (since they are cheaper than the 4770's).
4: Depending on your CPU you could run into a bottleneck.
lastly, i'm not being judgmental or trying to put you on the spot, if English is not your first language, that's alright 8) but we need to know more information about your machine to give you better advise.
To strait up answer your post though, i would go for the 4890 toxic, i've seen them at really good prices lately.
CPU: Well, damn, that's a good CPU so no need to worry about a bottleneck there 8)
MoBo: I will admit i am not as familiar with Intel MoBo's and chips as i am with AMD, but assuming the p45 Pro you are using supports Crossfire, then this should be fine. You really will want to check it (or if someone could chime in and say whether or not it does?)
PSU: Antec is a good brand and 650 watt should be more than plenty for either GPU option here. Although we could assume you have the necessary power connectors given the high wattage, it would still be good to check. The Saphire brand 4890 Toxic i see uses an 8pin and a 6pin. Where as the 4770's would each use a 6.
Overall, if you want to not deal with crossfire or you can't then the 4890 is a good choice. If you want to use crossfire and don't mind it, then the 4770's are better and will provide you with really good gaming power.
You still may want to consider waiting until the newer 5xxx series stuff comes out because one of those would be even better performance, or the older stuff should become cheaper.
so, if you don't mind xfire, and the mobo can handle 2 GPU's then
2x 4770 > 4890
if you already have a 4850 or a 4870 or something you could also just buy a second one of those instead and xfire them.