What kind of video card would be better for a media pc?

I'm building a pc that's going be running two 19'' monitors and an overhead projector. This is going to be an upgrade from an old sempron single core CPU with 2.25GB DDR400Mhz Ram and one AGP 512mb gddr2 and one PCI 128mb video card. The computer is going to have a quad core AMD processor (Phenom 9850 2.5GHz) and 4GB DDR2 800Mhz RAM. The only thing I'm wondering is which would be better for the video memory itself. I've narrowed it down between two options.The motherboard has PCI-E slots and is Crossfire capable so ATI cards are a must just in case we decide to add a second card later on.



My first video card selection was a Visiontek HD 3870 512mb gddr4 video card. Specs: 320 stream processors. 512mb gddr4 memory. Core clock unavailable, mem clock unavailable, 256 bit interface. I chose this card as a possibility because I have two running in crossfire in my home machine, they seem to preform decently with games but I wasn't sure.



Second option: Sapphire HD 4850. Specs: 1GB GDDR3, 800 stream processors, 625Mhz core clock, 1986Mhz mem clock, 256 bit interface. This seemed like a good media card because of the excess of memory and amount of stream processors.



If you could tell me which video card would be better for running the two 19'' monitors and the overhead projector (we play videos and announcements and such where we're using it) It would be greatly appreciated. If you can tell me of a different card that would preform even better than these (remember, ATI preferred) you can do that too. We're not looking to break the bank on a 500$ card, we're preferring to spend less than 140$ for one.



Oh, and a few miscellaneous questions for me that are sort of irrelevant. What exactly are stream processors used for? Like how do they function and aid the video? Why were GDDR4 video cards almost completely abandoned by ATI? Is there a major difference in GDDR3 and GDDR4? And finally is it better to have less faster memory in a video card or more slower memory?



Thanks!!|||Stream processors are the "single instruction multiple data" (abbreviated SIMD) processing units that actually do the computations for 3D graphics and visual effects like antialiasing. Video playback does not use these stream processors very much.



Unless you are going to be playing graphics-demanding 3D games on that machine, you don't actually need gamer-level cards like the HD3870 or HD4850. You can go with just midlevel HD4670s for video presentations.|||Just for a media PC then you can get by easily with the 3870, which would run cooler and also take less power than a 4850. But the 4850 is the much better card for gaming, but for just movies and such, the 3870 is going to be all you want it to be, it doesn't take alot of power for showing movies, it just takes good files. The better the file, the better the quality of picture...|||if this is a htpc neither one is really a good choice. good video cards for a htpc tend to be much lower-end because they're used mostly for playing back high-def video and even cheap video cards have built-in video decoders. also, noise and heat are very important in a htpc. ideally you want a silent, fan-less card for a htpc.

Stream processors are simplified processor cores on a video card. think of them as being like cpu cores, only far less powerful. they are also somewhat similar to the pixel pipelines older video cards had. gddr4 was abandoned because it did not provide enough of a benefit in terms of either speed or power comsumption over gddr3 while being somewhat more expensive. having less, but faster memory on a graphics card is almost always better than having more, but slower memory. the only obvious situation where more memory that runs slower is better is if the detail settings are turned up so high that the data won't all fit on the video card's frame-buffer. when this happens, the video card has to access main memory, which is much, much slower, 128-bit and 256-bit refer to the width of the memory bus. 256-bit provides twice the data rate and twice the memory bandwidth over 128-bit, all other things being equal. 256-bit is considerably more expensive, which is why mainstream and value cards were limited to 128-bit until recently (many mainstream cards are now 256-bit, like the 3850, the 4850, the 9600gt, and the 8800gt/9800gt/gts 250).