major difference would be the dual channel, which the 754 lacks. in praxis dual channel wont bring u much more speed but its nice to have of course. furthermore u can get an 939 board with nforce ultra or kt800pro chipset which means that it has 1000mhz hyper link. makes no sense for unocced systems but is nice to have. socket 754 and 939 are available with nforce 3 chipsets and chipsets from VIA aswell. if u go for the new nvidia nforce 4 chipset ur goin to have a different graphics card connector, called pci express. intel has this system already on many of there boards and its goin to b the future, the old AGP is almost dead, most cards will come out with pcie port and in like 1 year or so u b lucky to still get an agp card. uhm...what was my point....ya: if u choose nforce 4 it will have pcie system and iam not sure but here in europe pcie graphic cards tend to be cheaper than agp versions. via brought out pcie chipsets too, but i dont know when exactly the first boards will be available.
one thing i forgot to mention is that for socket 754 there are only Newcastle CPU`s. On socket 939 there are Newcastles (size = 130micrometer) and tehre are the newer CPU´s called Winchester (90micrometer). Winchesters are better cuz they consume less power, get a lil less hot and will be slightly faster (not much, like 2% or so). My advice to u to buy something like 3000+. The difference regarding speed to the 3200+ is less than the rating may tell, i mean, the 3200+ is not much faster, so if u want to save a lil money, better get a 3000+ and buy a nice cooler. If u really need extra speed u can overclock the 3000+ and again it wont matter if u take a 32+ or a 30+, cuz both will be nice to overclock. hope u understand my point

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so my advice, if u want to save each Cent go for an 754 board, i guess the 754 boards will be the cheapest to find. CPU prices are very similiar, 754 cpu`s and 939 cpus and even winchester cost all the same...maybe differences of some bucks. Concerning speeds: 754 systems wont be much slower than 939 systems, maybe overall 5%. If u have the money for an 939 system, dont hesitate and get one of these. Id suggest u get something like aMSI K8N NEO 2-54G Platinum S939 NFORCE3 ULTRA or an cheaper ABit AV8 with kt800pro. Both are excellent boards with all features. uhm...get a winchester CPU. if u go for socket 939.
If ur interested in buying an pcie graphics card like an 6600gt or better - its no problem with the nforce 4 boards just coming out these days. here in europe these are hard to get, costing about 130,-$ with SLI and the cheapest version without SLI for about 75 bucks - geze iam not starting with explaining SLI too....maybe u heard of it...pcie is working fine and i guess u wont need SLI already. PCIE is not better eg faster than agp at this point of time but it gives u more opportunities to upgrade ur pc when its necessary. same counts for 939 system, as socket 754 is slowly dieing and no more processor upgrades will come out for that socket.
ok, hope you understand my explanations...maybe not..but i swear they true

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