Would like some input on what I can do with my build

Put together my first rig a few months ago, been using it as a daily computer but now I'm bored and also, it's kind of a shame there's all this potential for power but I'm not utilizing it.

z68ma gigabyte motherboard
i5-2500k
500gb 7200.12 Seagate hard drive
2tb Western Digital Caviar Green hard drive
Asus GTX 460 (768mb) graphics card
stock everything else including CPU fans, case fans.
Antec 200 or 300 case
8gb 1333mhz DDR3 RAM
Dual monitors (Acer SL112 LED 22")
Dual boot OSX Lion 10.7.4 and Windows 7 Pro


This was a budget build. I was shooting for $400. Barely made it by $450 AFTER rebates. The rebates didn't come until a year later so I paid $500 or so cash. + $100 for the GTX460 give or take and I'm at about $550 for the entire build. Considering everything was new (just found deals and waited a long time for each component), I think I did okay price/value.


I'm new to OC but I understand the basic concepts of it by watching vids and reading a layman's guide article here on overclock.net. Basically you want your CPU to go faster, sometimes you have to raise the voltage to give it more power. But that raises heat. which can damage the chip. So it's a fine art (or science) of raising voltage, making the CPU work harder all the while providing it the much needed ice water and gatorade so it doesn't die on the football field. I kind of think of it like giving someone meth + nutrition&hydration but I could be totally off on the analogy.


Needs:
I use this computer everyday. It doesn't have any problems doing what I am doing now but it could be better. Daily tasks are something like Chrome open with 20+ tabs, probably 10 of them are youtube videos I "bookmarked" to see later in the day. Gchat always open. Second browser/2nd window of Chrome running Netflix on the other monitor. Playing Diablo III in Fullscreen Windowed while having a video or browser on the other monitor playing. Games, not so much but who knows if I'll start playing on the PC now since I got a decent graphics card.

I want to maximize everything performance all the while not giving up life on the parts and spending ALL LITTLE MONEY as possible. I would hate to blow up my rig that I spent months saving for and buying on a budget. And it wouldn't make sense to blow $200 on OC parts when I'm on a budget. (If i had $200 I'd probably just get a better graphics card and call it a day).


Questions:
I'm reading the i5-2500k can go up to 5.5ghz (in some) but usually something like 4.4ghz is more realistic.
- What clock speed should I shoot for? What's most common and will give me a huge performance boost from my stock 3.2gh while not having to spend lots to cool it? 4.4ghz?
- Given my needs for keeping price down, should I get air cooler or a water cooler? I'm not clear on the difference and when what is used for what. I just know water might be more expensive. The Corsair H60 liquid cooler is like $50 and so is the 212+ air cooler so not really sure.... I'm also very open to buying used so if something costs like $100 retail but I can get it for $40-50 used, its a viable option.
- I'd like to OC my graphics card as well to its potential.


Any pointers in the right direction will help a lot. Please feel free to tell me some parts are overkill for my setup/needs cause I don't want to spend unnecessary money.

Thanks. Do I need to (should I) get a different cooling fan or whatever for my GTX460 if I OC it?

also I forgot to add this in my OP but I was wondering which types of cooling is the most silent? A little fan noise is not bad. I have 2 stock case fans that came with my antec, and the stock i5-2500k Cpu fan, the PSU fan and the GPU fan and it's tolerable. But something that sounds like a little vacuum or a constant buzzing would kind of suck...

Ah, I thought so. Water cool just sounds badass but maybe I might not need it. Or the price wouldn't be justified in my case. I thought about RAID but 1 hard drive (Seagate) is currently only holding 500gb and running the OSX Lion. The 2 tb Western Digital is split into 2 partitions, 1 for Windows 7 and the other for all my data, music, videos, etc. A 3rd laptop harddrive 320gb, is used as a clone harddrive for Lion. I might look into this though.


Thanks. From what I heard, the 768mb overclocks better than the 1gb but who knows, could be dependent on my card. I'll try this and see what happens. Probably not worth the money to buy aftermarket cooler for the GPU.



I don't have the receipt anymore but...

Microcenter had a deal (and they still do sometimes) where if you buy a i5-2500k, you get $40 off ANY Z68 motherboard. If you buy the i7-2600k, you get $80 off Z68 motherboards. My z68 and i5-2500k came out to about $230. Motherboard also had a $15 rebate card. I bought the ram for about $45. Harddrive was $65 I think. I remember it was a great deal for the harddrive. Case came out to $45 (-$15 rebate), 500w PSU was $50 or so (-$10 rebate). That's $435 or so. Minus $40 in rebates. I think im missing something here but it was around $450 out the door and $40 in rebates. Plus I bought a 8gb USB stick, an anti-static wristband, sata cables and stuff. The 2tb western digital drive was less than $70 on a Slickdeals that staples had going on on the 2tb Western Digital Elements external harddrive. You can open the external and inside is a perfectly nice WD Caviar Green (or black if you're lucky) drive.


Gotta search the used market now!