H80i works if you have a 120mm fan mount. H100i is the best but you need 2 120mm fan mounts that are right next to each other as if they were best friends! H100i is only for extreme overclocking really, H80i will keep your CPU cool & at a high clock like 4.5GHz.
It completely depends on what you mean by watercooling. If you mean a closed loop system then the best you cold do is the h100i. Here is a page about how and where to install various closed watercooling systems in a level 10 gt http://www.hardocp.com/article/2012/09/26/thermaltake_l.... However, the if you want the absolute best watercooling there is, that would be a custom water loop. A custom loop will take planning and cost quite a bit more, but you will get lower temperatures and you can add your gpu to the loop. I would also recommend looking into high end air cooling for about $30-$50 you can come within a few degrees of the far more expensive closed systems. But, if you really want to watercool, your best options are the h100i or a custom built loop. The h100i will fit in your case, and is only slightly more expensive than the h80i so the h80i is somewhat useless in your situation.
Also I'm sure you already know this, but, if you do not plan on overclocking your CPU any upgraded cooling will be a waste of money.