Crossfire - i need advice >.<

Hi peepsIve currently got an overclocked hd4870 512mb   and im looking to crossfire it with another hd4870. Ive got my eyes on a palit hd4870 1GB for 180quid.  Im unsure about how they will perform together as 1 is 512mb and the other is 1gb.  Im i right in thinking that the 1GB card will only be able to use 512mb because the other card is only 512mb, or will i get 1.5gb (1gb+512mb)?there is very little price difference between a 512mb and a 1gb card  soo i thought it would be worth getting the 1GB card if it will perform at 1GB.i dnt have any experience with Crossfire or SLi   so any advice/help would be much appreciated.  Thanks in advance.(also will my C2D E8400 @ 3.8ghz be able to keep up with 2 hd4870's?  )

Buy another 512meg card.
The extra 512 meg will not be used on the 1 gig card.
Both cards will run at the specs of the lowest clocked card.
Your best bet is to buy another exactly like the one you have.
Your processor is fine for Crossfiring a couple of 4870's.

With Crossfire you need to remember that when you connect the cards it does not combine the memory only the GPU's work together. So if you have a 512mb card and Crossfire it to a second 512mb card your total avalible memory is still only 512mb.

You can Crossfire the 1Gb card with the 512mb card and if you do it right have 1Gb of total combined video memory. To do this the 1Gb card has to be the master (the card with your monitor connected to it) and the 512mb card just used for its GPU.

Also you need to remember that if you have two cards with different core clock speeds and memory speeds Crossfire will default to the slower speed of the two. So keep that in mind when looking for your second card.

ok thanks stoner133.
i always thought that all the memory from both the cards would combine =/
ive decided on a card. its factory OC'd to the same spec as my current card so hopefully they will run at the same OC
heres a link: http://www.in-pcs.co.uk/product/Pa [...] _6464.html

so effectily i will get 1gb of video memory?(512mb + 512mb) or just 512mb? im so confussed now:S
if all i will get is 512mb of video memory then i wont bother its just not worth 370 quid
i might aswell try and sell my hd4870 and save up for a hd4870x2

i r so confussed can someone clear things up ?!?

If your board only has one 16X and one 8X lane your going to take a hit since both lanes will run at 8X under Crossfire. You best bet with a board like that is to get a 4870X2 and just use the 16X slot.

Will be interesting to see what the difference shows up to be.

The cards will each use 512 meg of memory. But it is not combined. You do not have 1 gig effective total, you have 2 cards each using 512meg.