USAFRet :
NewXeneration :
Never buy a software before hardware. But that's me, i'm not telling you to not go with confortable not modified windows, instead of going with an Open OS with modified core, while you get the money to buy it.
Never waste extra money on software; only if you need it.
An "Open OS with modified core" ?
Care to expound on that? Because I've never heard of anything like that associated with a legit Windows OS license.
Hardware before software?
In the OP's case, a 120mm Kraken is no better than a typical air cooler. IOW, a waste of money. The H80i is no better.
Buying a valid software license is not a 'waste of money', if you actually use that software. Like using the OS, which operates the whole system.
First, i'm not saying that that Water cooling is better than an air colling, which i preffer most of time. Also i'm sure you know there are many options for an open source OS. You can emulate almost anything you need on that, or even run windows on it in a VM. (You can pay the license if you want on it).
As i said, from my point, there's no need to waste on software if you have your needs solved already. It's always better to pay for hardware.
If you NEED, to go for windows, go to the cheapest license you can get. Most of time i find myself using unix based system with a modified kernel to manage server applications. So the cheapest Windows license should solve all your needs.