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Pcie x16 slot split over 2 x8 slots performance

Last response: in Graphics & Displays
January 30, 2009 10:10:22 PM

unfortunately my motherboard (MSI DKA790gx) has 2 pcie slots with crossfire enabled, but is limited to 2 x8 lanes when 2 cards are used, and one x16 when one card is used. I am wondering if this will degrade performance much when using 2 radeon hd 4850's such as this one:
I can get 2 of them for less than the cost of a gtx 260, which is what i'll probably get if I decide to use just one card.
can someone help me out on decidng which to get? i'm really leaning towards nvidia, as most games I will play perform better with them, but I am certainly open to ati if I can get more performance for the same money.
Now, honestly, who designed this motherboard... first, the ram slots are too close to the cpu socket, so when using a performance cooler it has to be put on backwards, so it blows toward the front of the case.
second, the pcie setup is like this:
top: x16
2nd: x4
3rd x4
4th x8
with no space between the bottom x8 slot and the pci slots. so when using 2 cards that take up 2 slots each, theres an extra slot above the second one and it disables one of the 2 pci slots which I need both of. this would take an extra investment of a usb wifi card or tv tuner, whichever is cheaper. I wish I had bough a proper designed sli board, but I hadnt dreamed of using 2 video cards when i bought it, and the motherboard was a steal at $85.
January 30, 2009 10:54:31 PM

heh, your right, I just guessed, as I am not using them and dont plan on using them anyways.

looks like I could run dual 4830's for $160 or so. what kind of performance decrease would this involve over dual 4850's? and again compared to the gtx 260
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January 30, 2009 10:56:02 PM

4830's in Crossfire is a good setup. They will top a 4870, GTX260 as well more than likely. Also some of the 4830's can overclock to a 4850 if you can keep temps undercontrol and stable.
January 31, 2009 4:35:42 AM

well, 4850's have come down enough in price I think I might as well get those. the first one will likely be an asus overclocked model running at 680 mhz. Due to my motherboard configuration, I would like the second one to be a single slot one by MSI. This one runs at the base clock of 625 mhz. Will this be a problem?
here are links to the two cards:
January 31, 2009 6:52:52 AM

his one is nice, I looked at it, but quite a bit more expensive. I am trying to keep this under the cost of a gtx 260 so I can justify it hehe. The MSI I chose for the one slot size, as my second pcie slot is right next to where my precious 2 pci slots start. I have a wifi card and tv tuner. I dont want to resort to usb for either of those.
Also the asus card I listed (overclockec at 680 mhz) with a silly looking fan is only $110 open box right now. HIS makes a one slot 4850, but its more expensive. anyone have experience with any of these cards? or an answer to the one card factory overclocked, one card base question?
January 31, 2009 6:58:04 AM

thes setup should also be considerably cheaper than a 4850 x2 at $~300. the sapphire one has quad dvi. this is nice, especially because crossfire currently dosen't support dual monitors, let alone quad monitors :)