my gpu is a Sapphire HD 5850 along 4GB ram and a quad core cpu 2.4GHz
usually i get 55fps with high settings
with ultra and texture pack and like 50mods i go usually down to 30fps
if i set a little better shadows and turn on ENB with SSAO only actived my fps goes to 19fps most of time

IF i buy a second 5850 will i get visible benefits?
(probably i wont get precise double fps with 2 cards, but how much?)
crossfire is working good for skyrim?

i need some suggestions

You will likely hit a cpu bottleneck with xfire 5850's.

What % of your gpu does skyrim use now?

Edit: what is your quad ? Q66xx?

how to see how much % GPU is used by skyrim? i have no idea

MSI Afterburner.

my pc:
CPU: AMD Phenom II X4 945 3.0G
RAM: DDR3 2x2GB 1333MHz Kingston
MAINBOARD: ASUS M4A785TD-V EVO

after the post of PhonAntiPhon (thanks for make me remind me it) i tried to overclock my GPU. i only switched up the clock to 775 and the memory to 1125...(what are the risks in overclokking? sorry ot)

running 1920x1200 + 0AA + 16anisotropic + ultra settings + texture pack + 50ish mods + medium SSAO (ENB) + some shadow tweaks like shadowmapresolution to 6144
i was around 25fps but probably it was a luky place
my GPU was at 100% working, in my cpu the 4 cores was at like 40% and the ram 2.67GB used of 4GB total

so...with my pc, is an achievable idea to put in crossfire 2 sapphire 5850?
in skyrim an/or other games i will get relevant benefits?

Skyrim is very CPU dependent. You will get the most benefits by upgrading the CPU rather than the GPU. We are talking pure gigahertz here. The more the merrier. I believe you will really only see a significant boost in fps if you get a high end graphics card and play in high resolutions with the HD pack.

The 5850 has 1GB VRAM right? Might be borderline or just a bit too little for HD pack. Others can probably answer this better than me.

Most other games on the other hand will surely see a boost (provided they support Crossfire). But the 5850 is an aging card now and will probably not be the best investment in the newest games that use DirectX 11.

thanks for the answer, but sorry, i cant undertand it
first u say its better to buy a new cpu
just after you tell me that i'll get more fps with a new gpu....

as i said, during a medium-strong scene i have the cpu working at 40% and the gpu at 100% , from this point i'm thinking the cpu is not much stressed, i cant belive the fps drop is caused by the cpu... while the gpu at 100%
im thinking to change te gpu as u say, but.... if i can get a second 5850 for crossfire for like 90bucks... im just evaluating this possibility...

the 5850 DO support DX11 > (i hope there is not a problem to link this: http://www.sapphiretech.com/presentation/product/?psn=000101&pid=286&lid=1 )

Let's put it this way: If you play with HD pack, several texture mods and high resolutions (and maybe increased ugrids) then you will benefit from having a powerful graphics card with a lot of VRAM (see here: http://www.anandtech.com/show/5699/nvidia-geforce-gtx-680-review/15). But I'm not sure if the 5850 is the right card for that, even with crossfire. And you wil still need a powerful CPU if you want high fps.

I have two 5850s myself. Well, not exactly. It's a 5970, but it gives roughly the same performance as two 5850 cards. I used to have an i7-860 @ 2.8GHz. When I upgraded to an i7-2700K and overclocked it to 4.4GHz my fps skyrocketed. Which shows that the game is heavily CPU-bottlenecked, not GPU.

But will you get a boost from using two 5850 in Skyrim instead of one? I don't think you will get a noticeable boost really. When Skyrim was released it didn't support Crossfire. Which means it used only one of the GPUs on my 5970. But when the drivers were updated to support Crossfire, I can't really say I noticed a significant increase in fps.

But in most other games you should get a nice boost with a second 5850.