They seem very evenly matched TBH:
http://enthusiast.hardocp.com/articl...50aHVzaWFzdA==
http://www.hexus.net/content/item.ph...=17863&page=22
http://www.techpowerup.com/reviews/S...D_4890/33.html
http://firingsquad.com/hardware/ati_...75//page14.asp
http://www.pcper.com/article.php?aid...=expert&pid=11
http://www.guru3d.com/article/geforc...review-test/20
http://www.anandtech.com/video/showdoc.aspx?i=3539&p=22
The GTX275 does seem slightly ahead but the differences are tiny at higher resolutions and settings(where these cards ar going to be used TBH) and the peak power consumption is quite high too.
Idle power consumption of the HD4890 seems to be the same as the HD4870!! However peak power consumption seems only slightly higher and is in fact much lower than a GTX275!! Seems there have been some improvements in power efficiency in the cards too!!
Seems most RV790 cores will do 900mhz+ easily!! It also seems that it has a few million transistors more than the RV770.
Edit!! Regarding power consumption this review says that it is actually lower than an HD4870:
http://www.xbitlabs.com/articles/vid...0_6.html#sect0