RV740 is often misunderstood as the successor to RV730 which in fact is far from it. RV740 is expected to take the market by storm by Q2 next year as the best value/performance chip from AMD. It is AMD's first 40nm GPG chip with all IP being re-designed and characterized for 40nm.
If you check out the chart above, RV740 is essentially a 40nm version of RV770LE core with 640 stream processors but has the goodness of the GDDR5 memories used currently by the HD 4870 card. Certainly, AMD reckons that 128-bit memory interface is sufficient for RV740 by using the GDDR5 memories. You will also be seeing RV740 cards with GDDR2, GDDR3 and even GDDR4 memories to give you more choices.
Due to its 40nm process, power consumption clearly will be much lower than HD 4830 yet faster. Performance of RV740 is estimated to be between HD 4830 and HD 4850. You can expect RV740 cards to be priced lower than US$100.
if that turns out to be true,ati have a killer card on their hands.