With an i5 750 processor, and an Ati Radeon HD 5850, which Motherboard(And memory) should I choose?
I mean, the brand.. I'm pretty sure I'm going for a P55, it's the best for i5 right?
I think the options would be Gigabyte, Asus and MSI.
I want a crossfire ready motherboard, so that I have the option of trying out 2X5850 later(though I probably won't)
6 USB ports minimum..(does that really depend on the motherboard?)
Also, I wanted to know how many PCIe connections there are in a standard P55. I mean, can I add 2 Graphic cards, along with a TV tuner and maybe a LAN/Ethernet card?
About the memory.. I don't know about brands, I think Kingston is good, and corsair(If i can get it)
But the real thing is how much.. is 4GB DDR3 ok for games like GTA IV, or do I go for 6GB? Is it worth it?
The ASUS P7P55D-E Pro should be your motherboard of choice - it has two PCI-e 16x slots, perfect for CFX, and considering that your HD 5850s are dual-slot, you'll still have two PCI-e 1x slots and one PCI slot for further expansion, after adding the two HD 5850s. Comes with SATA III and USB 3.0 too. It has six USB 1.1/2.0, two USB 3.0 and three more headers which would come out with six USB 2.0 headers, so that satisfies your USB requirement.
Well, 4GB DDR3 RAM is plenty for most of today's games, and 6GB would only run in single channel, which may hinder performance, although now by much, and if you wanted to run 6GB in dual channel, you'd need a 2x2GB and 2x1GB kit which means that you won't have any slots left for memory expansion later on. Just stick with 4GB, and I suggest this kit - the G.Skill Ripjaws 2x2GB DDR3 1600MHz CL8.
I have the same cpu and gpu. I purchased the MSI P55GD65 mobo and it is great. Easy for overclocking, a ton of USB slots, 2x ethernet connects, high def audio outputs including optical, 2x PCIe slots with a max 16x (16x/0 or crossfire 8x/8x) which is perfect, and it has a lot of other slots for any other cards you might want to install. It's also a bit cheaper than the ASUS board mentioned above.
For RAM, you'll need to use either 2 or 4 RAM chips in order to take advantage of dual channel. 4GB is generally more than enough, especially just for gaming, otherwise go with 4x2gb for 8gb total and not 6. 6 is more for triple channel RAM, which is supported by the i7 series. The RAM I bought, Patriot Viper II Sector 5, was only about $125 ish and it performs really well, 1600mhz 8-8-8-24 timings. If you read some reviews on it, it's generally rated quite well. GSkill is supposed to be good, but it's a newegg house brand so if you want to purchase somewhere else, you can't get it. Personally, I priced my PC out on Newegg then went to a local retailer and got everything for either a bit less, or price-matched plus didn't have to pay for shipping nor wait a week or two for the stuff to show up so all in all it was a lot better for me.