Your planned rig will 5-box with ease:

My planned rig:

Processor: I7 2600
MB: ASUS P8Z68-V PRO/GEN3
Ram: 16GB
Primary HDD: Crucial 256GB SSD
Secondary HDD: WD Black 1TB
Video: 2x 295 GTX (non-sli, dedicated physx 2ndary)
OS: Windows 7 Pro
IO: G510, Evoluent left handed edition
Case: Antec 900
I have a similar system.

Same CPU, same motherboard (but Generation 1), same OS, same case.
I'm using 8GB of 1600mhz ram, my wow and OS are on separate SSD drives.
I have a 1GB GTX 570, for my video card.

The i5 2500K was fairly smooth until I started to stream.
The i7 2600K is totally smooth, with or without streaming.

I play with the slaves on lower settings (except view distance, which is medium).
And the main on 3/4 settings, except view distance maxed.

You can check my stream site, there are videos there.
To give you an idea of my quality/performance.