That's not always the case, though, icepac.
With each successive generation (first digit) you get improvements in the architecture, improvements in the card layout and overall capabilities.
While the speeds and the clocks might not increase much, the 5000 are more capable than the 4000, and the 6000 more capable than the 5000....
So no, you can't just say as a rule that means the 4890 will out muscle the 6770.
The second digit does usually indicate whether it is the standard gaming card or the budget line. 6770 is the stripped down version of the 6970, for example. Often they save money by having slower RAM (128-bit instead of 256 or 512 bit or whatever). Sometimes the extra speed can overcome the slower RAM.
A bit more "super generic blanket statement" guidelines are: there is the standard card, where the third digit is "7" (i.e. the "70" cards) and there's the slightly-more-budget usually of lower clock speeds or some other features, where the third digit is "5" (the "50"s) and then there's the high end overclocked or super beefed up variants that have "9" ("90"s)
So a 4890 was the highest top-end of the HD 4000 series, generally speaking. The 6770 is the standard of the stripped down budget-gaming cards (but still gaming, not for desktop publishing or corporate life!).
Even so, because of 2 generations of GPU development between these 2 cards, the 6770 is half the price and just about as fast as the 4890.
http://www.gpureview.com/show_cards.php?card1=608&card2=658Check it out! Interesting, no? 4890 definitely has more memory bandwidth, but all the clocks, the performance specs for any criteria, they are even or on the side of the 6770. That newer architecture does have its benefits. Compare same-classes (4890 to 6870) and the new ones blow the old ones away.
I know this doesn't help narrow down the issue at all. Hopefully it adds a little flavor to the topic.
For the sake of narrowing down the issue: The 6770 is a fine card with very nice performance. It will out perform what you are replacing. It's half your budget, as well. Or talk to ebfd11 and see what he has in mind for his 2 cards.
I don't think you can go wrong with those 2 options.
