I let you in on a little secret, airflow and direction is more important than how much you are flowing as long as it adequate. (so don't worry about not being able to fit that bigger more powerful 120mm fan)
For your case I think a CPU cooler that has a somewhat simmilar design to this where the heatsink is horizontal would probably be the most beneficial when you set it up to exhaust up into your top 230mm fan. Don't know how well this works but it gives you an idea of what I mean here is the link.
I mention this because I use to use a cheap case with my aftermarket cooler that should have exhausted most of the heat directly out of the case but about 50% of the air flow was easily obstructed due to the thick grill so after awhile I noticed most of the heat collected to the top of my case and was exhausted by my weak PSU fan which was mounted above it. I think you may run into the same problem with trying to use the 2 60mm rear fans to exhaust your CPU's hot air.
So with any luck you have a direct shot from your CPU to the top exhaust fan, as the pictures of the case I've seen only give me so much of an idea of what it be like installed while you have it in front of you.
As for the best cooling, there are websites that rate the CPU heatsinks, google it and you should find it as there are a few of them out there.
Oh and on a final note water cooling properly takes a lot of money to do properly and last I check a few years ago most of those pre-built kits, etc were horribly done and a good/cheaper air cooling can do better. Where this truely shines is in the well researched and custom water cooled setups (which typically can get expensive I hate to say), and fitting a good water cooling setup in such a small case would be quite the challenge.