HUGE Upgrade guidence

[Ex7ra]

==CURRENT SPECS==
CPU- Intel Core 2 Quad Q8300 (2.5GHz)
Motherboard- Foxconn P43AL
Chipset- P43 + ICH10
Memory- 6GB DDR2 800MHz (4 memory slots. Max 16GB)
Hard Drive- 1TB SATA Western Digital Caviar Green
CD Drive- LG GH40F DVD±RW
Video Card- NVIDIA GeForce GTX 560ti 1GB
Sound Card- Realtek ALC888S High Definition Audio
PSU- XFX 650W
.
The things that i want to get are a new processor, a new motherboard and some new RAM.
My budget is £300 - £400
Ive looked at the i5 2500k, its expensive but good.
I use my PC for gaming and the occasional video rendering (rarely)

So my question to you is, what mobo, cpu and ram should i get? and will i need a new heatsink and OS?
(im selling my old mobo, ram, cpu and heatsink to my lil brother)

 

[Graphite946]

If you keep your hard drive, I wouldn't worry about needing another OS. Your brother will need to buy his own, along with a hard drive for himself.

What vender do you have a preference to buy from? What size MB? Are you going to overclock?

 

[Ex7ra]

MY little brother has a PC, all be it a really bad one (designed to be a family PC, internet shopping etc) so couldnt he use that HDD? i also have the recovery discs that i made as soon as i got my PC, could he install windows of them? (the ones that i use to reset to factory settings / re install windows)

now, preferences...
im happy to buy off amazon, but so long as the seller is amazon,
and i have a local PC world, so there is fine.
my dad knows a few sites that he says are good, here they are:
http://www.scan.co.uk/
http://www.dabs.com/
http://www.ebuyer.com/ <-- (i think)

 

[Graphite946]

Look into newegg also.

For the OS, if the computer he is using now is a pre built, he will not be able to reuse it outside of the pre built setup.

I would recommend buying a new copy of windows 7, or having him try out the windows 8 preview.

 

[Ex7ra]

I wouldnt really want to buy from anywhere that is outside of the UK at this time, as it makes returning things if they are faulty a real hastle.
-
Does anyone have any ideas on a CPU, mobo and RAM that i could get? for a suitable price that is, and if i need a new heatsink of it the CPU comes with one.
EDIT:
ive been looking around, and i come across this: http://www.amazon.co.uk/Gigabyte-GA-Z77-D3H-SKT-1155-Z77-D3H-Motherboard/dp/B007KHROSC/ref=sr_1_1?s=computers&ie=UTF8&qid=1342732271&sr=1-1
http://www.amazon.co.uk/Intel-Generation-i5-3570K-3-40GHz-Technology/dp/B007RUZKK6/ref=pd_bxgy_computers_text_b
http://www.amazon.co.uk/Corsair-CMZ8GX3M2A1600C9-1600MHz-Vengeance-Memory/dp/B004CRSM4I/ref=pd_bxgy_computers_text_c
.
If anyone can see any cheaper alternatives, without loosing much / if any performance, please do say so.