My first PC Build ($750 - $850)

That Antec is made by the best SEASONIC.

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-3570K 3.4GHz Quad-Core Processor ($214.96 @ SuperBiiz)
CPU Cooler: Xigmatek GAIA SD1283 56.3 CFM CPU Cooler ($31.99 @ Newegg)
Motherboard: ASRock Z77 Extreme4 ATX LGA1155 Motherboard ($99.99 @ Newegg)
Memory: G.Skill Sniper Series 8GB (2 x 4GB) DDR3-1600 Memory ($84.99 @ Newegg)
Storage: Seagate Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($85.53 @ Amazon)
Video Card: PowerColor Radeon HD 7870 XT 2GB Video Card ($197.98 @ SuperBiiz)
Case: Cooler Master HAF 912 ATX Mid Tower Case ($49.99 @ Microcenter)
Power Supply: Antec High Current Gamer 620W 80+ Bronze Certified Semi-Modular ATX Power Supply ($64.99 @ NCIX US)
Optical Drive: LG GH24NSB0 DVD/CD Writer ($14.99 @ Newegg)
Total: $845.41
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-12-05 19:38 EST-0500)

Well I'm no programmer so i really couldn't tell you, but i don't think there would be much difference in compiling time between the two, maybe if the software is biased? i think there was something about intel making a compiler that purposely ran worse on non intel chips, but anyway, I doubt it would make much difference, but if you want an intel build you could go with several options

this one http://au.pcpartpicker.com/p/2fSQS you have to drop your 7850 to a 7790 to get an i5 like you wanted.

the second one http://au.pcpartpicker.com/p/2fSVt you can keep your 7850 but you have to drop down to an i3

and the third option http://au.pcpartpicker.com/p/2fSZa you keep the i5 and 7850 but you get a slightly different motherboard and lose your aftermarket cooling and rely on the stock cooler.

You could save money on all of these by going to a b85 motherboard though, they are more on the business side but if they work for you why not use them, you could save $10-20 probably by going to a b85

Well I can't tell you exactly how different they perform, but this should give you a general idea of what fps you "could" get http://anandtech.com/bench/product/776?vs=778

it looks like crysis is the only game on that list that you play unless you meant crysis 3, but anyway im sure it will give you an estimate on the difference in the 2 cards, an 7850 is definitely better. It's good that you could lower the 2TB drive down, i figured you needed that much space for something like movies you had so I left it alone.

Here is a build that is at your max budget, you get an i5, an HD 7850, and a slightly better motherboard

PCPartPicker part list: http://au.pcpartpicker.com/p/2gke5
Price breakdown by merchant: http://au.pcpartpicker.com/p/2gke5/by_merchant/
Benchmarks: http://au.pcpartpicker.com/p/2gke5/benchmarks/

CPU: Intel Core i5-4570 3.2GHz Quad-Core Processor ($222.00 @ CPL Online)
Motherboard: ASRock Z87 Pro4 ATX LGA1150 Motherboard ($130.00 @ CPL Online)
Memory: GeIL EVO Leggara Series 8GB (2 x 4GB) DDR3-1866 Memory ($95.00 @ Scorptec)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($67.00 @ PLE Computers)
Video Card: XFX Radeon HD 7850 2GB Video Card ($175.00 @ PCCaseGear)
Case: Cooler Master K380 ATX Mid Tower Case ($54.00 @ CPL Online)
Power Supply: Antec High Current Gamer 520W 80+ Bronze Certified ATX Power Supply ($85.00 @ CPL Online)
Optical Drive: LG GH24NSB0 DVD/CD Writer ($22.00 @ Mwave Australia)
Total: $850.00
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-12-07 16:36 EST+1100)

Now I'd like so say that's all, but from what I've noticed I haven't seen a single thing require some kind of shipping so I'm wondering if pcpartpicker doesn't have an estimate on what shipping would cost in Australia. so if that's true you could be way over budget if you add the cost of taxes and shipping

If it is you could try lowering to an i5 4440, its cheaper, the only reason I chose the 4570 was because it has a higher boost clock at 3.6 Ghz and the 4440 is 3.3 ghz but its up to you if that extra power is worth $17. you can also move down to the 7790 if you need to save money you can refer back to that link up top to see what you would be losing gaming wise. and lastly another way to save money is to get a different motherboard, either an h87 or just a cheaper z87 if you'd like, the z87 is in the more performance and gaming side of the motherboards while the h87 is like your normal everyday kind of one but if you're on a budget it could work for you