The Hd 5670 is (as everyone said) a good balance between gpu power and memory bandwidth and if you cant get any better you should certainly go for it.But i would really prefer stretching just some hundreds of rupees to get that GTS 250.(and believe me there will be no power issues because i have been running a gts 250 on a 450 w psu for 2 years and no problems whatsoever) And now about the difference in gddr3 and gddr5 memory.its actually pretty simple and i will be showing the difference through the example of HD 5670s memory(GDDR5) vs GTS 250s memory(GDDR3).so here it goes :
First of all: do not believe the "clock speeds" for GDDR5 . The baseline clock speed of GDDR5 is always the same as GDDR3; GDDR5 simply quad-pumps the data clock while GDDR3 dual-pumps the data clock.(remember how DDR2 ram is not running at double the speed of DDR ,but rather sending double the amount of information via every megahertz?) so the bottomline is that if GDDR3 memory is sending 2 data per clock ,the GDDR5 is sending 4 data per clock.
GDDR3 = 2 data per clock.
GDDR5 = 4 data per clock (with additional latency overhead over GDDR3).
But this is not all and the fun arises here. The thing is that the frequencies are not the only thing in play. The bus width also matters. The buses are like highways, letting data to move from here to there.so the higher the number of lanes, the faster the traffic moves. So,GTS 250’s GDDR3+ 256-bit bus width is roghly=HD 5670’s GDDR5 + 128-bit bus.And the official specs of the cards seem to confirm this.The memory clock of GTS 250 is 1100 mhz, in effect it is 2200 mhz.now memory clock of hd 5670 is 1000 mhz,but in effect it is 4000 mhz.so the GTS 250s memory clock is running at approx. little more than half the speed of hd 5670s but because of the double bus width of GTS 250 it is just slightly better than HD 5670s.the memory bandwidth of HD 5670 is 64 gb/s while GTS 250s is 70 GB/s. See the connection now? so what does GDDR5 mean if we can just obtain same results with fatter buses? It means that they can offer you a higher-performing card than the GDDR3 cards without going to a fatter bus.the GDDR5 allows one to make faster cards with the same frequencies as GDDR3s.The key to GDDR5 is enabling the NEXT generation of graphics cards without the need to go to even fatter buses, and reducing the memory power consumption vs GDDR3. It also allows the creation of cheap 128-bit enthusiast cards(which is never possible in GDDR3).The GDDR5 memory also reduces the complexity of cards than in the GDDR3 cards because GDDR3 needs many more things to sustain their high speeds than GDDR5.GDDR5 allows for cheap and better cards than GDDR3.
Conclusion : The GDDR5 is the future as the DDR2 was for DDR RAM and now DDR3 is for DDR2.And while the HD 5670 is a good choice you can get a faster GTS 250(it has GDDR3 i know,but i explained why its still faster and what all matters,read the explanation if you haven't already) for some few extra hundreds and they are a hell lot of worth it with your quad core processor.
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with your proccy the HD 5670 will be the weakling that's all(and i don't want you to settle for only a good enough gpu although your budget is tight.).and i have made the difference between the GDDR3 vs GDDR5 memory pretty understandable ,i hope you get a clear picture now.if you have further confusions don't hesitate to ask me.you can PM me too.
