faster processor is always better. and for only $15 more, no reason not to go with a faster one.
I only buy Asus motherboards. Asrock is kind of a no name company. Might be fine, might not. I don't have any experiance with them one way or the other. Featurewise it looks comparable.
Ram, 4 smaller sticks speedwise would be slightly better than just 2 bigger ones. the reason I suggest the two bigger ones instead is because if you add two more of them a month later, photoshop will useevery bit of ram you can throw at it. the speed loss in the short term would be overruled by the cost savings of adding more ram later. if you don't intend to do that then yeah, go with 4 4GB sticks. Ram is still dirt cheap and easy to source though,
Water cooling is a very god investment if you are overclocking. If you are planning to take your voltages that hight though keep in mind it probably isn't the CPU that is going to cook first. it's going to be your motherboard chipset or your ram. ram water blocks and motherboard water blocks do exist, but they are expensive and kind of a pain to install. BUt also effective. I ru mainly koolance stuff in my boxes. Swiftech is still excellent too. If you do go into water cooling, be sure to get as many koolance quick disconnect fittings as possible for your lines. Makes swapping out components later on much, much, much easier. Also when it comes to water blocks specifically, consider used equipment. the "good" water blocks don't readily fail, and are generallt easily rebuilt. Picking up a Koolance 360 CPU block for example used would save you $70 over the retail new in box $370. Same thign for fittings and reservoirs. Pumps and controllers you definitly want to go new, and you definitly want a controller rather than just running the pump flat out. Also keep in mind that video water blocks generally start beign effective only for the larger, more popular upper end GTX series or ATI series cards. The generic "one size fits all" or hybrid VGA coolers aren't worth their weight in scrap paper.
I tend to use newegg alot. tigerdircet or even CDW occasionally have better prices on individual components, so it is certanly worth taking a look. I find the conveniance of having all my parts on one invoice in case of RMA and shipped generally in one box tends to offset the $5-$10 I would get ordering elsewhere for me.