I'll jump into here with this:
I built a system last year...Waited and waited for
the i5, i7 prices to drop I chose to go with an i5 chip that was on sale and fortunately that was good decision because it's never been that price again. AMD is a good company but I trusted Intel,
i-5 3750K unlocked cpu quad core 3.4ghz
Xigmatek Loki II cpu cooler
ASRock Z77 Pro 4 mb - took a chance on them after using Giga & MSI and have to say ASRock rocks !
16 gb ram
Corsair
XFX Fanless Video card I needed multiple monitors so i went with this card to keep the load off the cpu.and reduce fan noise in case
Lacie Firewire pci card TI chipset for interfacing the Focusrite units I have.
120 gb SSD: system drive and DAW software
2 - 500 gb 7200 rpm drives for samples and final mixdowns etc... this config will change though
650 watt Corsair psu A pretty quiet unit
DVD read write drive
Cubase 5 for now with various plugins,
Wavelab 6, and other related software.
WINDOWS 7 home prem
all in a Rackmount case with heavily modified venting and drive bays
This system was built for under $750 but I watched sales like a hawk Newegg and MicroCenter were the suppliers
Had bought the rackmount case off Ebay a while ago in anticipation, it gave me some headaches when fitting the MB into it .
But I have a full shop at my disposal so it was nice to be able to 'custom retrofit' and devise a nice cooling fan airflow scheme.
So be cautious if your looking at rackmount cases and make sure your MB will fit and mount up properly
Now to chime in with cali_afroman's reply
HEAT is one factor to consider. When choosing a cooling scheme i went with Xigmatek cpu fan and one 120mm case fan which is working well.
throw away any stock pu cooler that is packaged with them they are noisy will fail sooner than later and will not provide good cooling when the unit is running for long hours. Airflow thru your case is something that should be addressed
Ram: more is better and the prices are lower then they've ever been.
An SSD system drive is a great thing no noise no heat = a happy machine and a happy user.
I have not used them for the heavy writing that project storage and rendering drives see so the debate is still ongoing for that.
You will read alot of info about read write events on SSDs and their limit on them advice : research and ask.
As for the MAC vs
Windows well that is a personal choice and i won't get into that whirlpool argument here.
I am using Firewire pci card since i have
Focusrite Saffire gear i have absolutely zero issues with firewire.
Safeguard yourself by getting a firewire card with the texas Instrument chipset in it.
If you go USB then consider keeping other USB peripherals at a minimum as they will contest for transfer lanes within the mb
There are few USB 3.0 interfaces out there right now and with Thunderbolt format on the horizon we may not see many more.
A good research on that is worthy Google these topics there s alot of info out there
You wont need a soundcard if you are using an outboard interface and most MB's have onboard audio ( but this is not sufficient for DAW work)
I researched and also looked at what the 3- 5 DAW build companies were using It was a painstaking process
But I wanted to be sure of my choices in order to futureproof my machine to have years of use without any problems.
Above all else keep asking questions here and elseware so you can get a good across the board idea of what you want