This will be a long answer and I am hopeful you read the entire post.
There are many ways to do air flow and water loops. The reasoning behind me exiting the air through my radiators is that I do not like dust. I work hard at keeping dust out, as it the enemy of a system. It can reduce the efficiency and reduce the life of the equipment. Bringing air into a case from the radiators does help them cool the water better, but you lose the temp gains with the hot air from the radiators exiting into the case. Also, you need to clean the radiators more often, since there will be considerable dust build up on them since it is the air inflow and the radiators act like a filter picking up the air particles given the positive charge of the radiators metal. This is not to say my configuration does not have dust build up, but it should be less if I have been effective with limiting the dust inflow. Even when you bring air in from the top, you get a considerable amount of particles and dirt which will build up on the radiators, which also reduces the effectiveness of the radiator since the dust build up insulates the radiator and actually will hold heat in. This all my opinion, so it is not meant not to critique your set-up. I believe in getting information, both good and bad, and then determining the path. How often do you clean your radiator? It would most-likely need it every three months, but will vary based on where you live and the time of year (Spring and Fall being more often given the pollen build up outside). An effort that I am unwilling to do, especially since I like playing games and doing family things more than I like breaking my case down, draining my loop and cleaning my components. Since my I did my set-up over the Christmas holiday in December, I have yet to drain it and clean my components, but will within the next 30 days. I will have a good idea if my positive air flow configuration works in limiting the dust build up, but from my observations so far it looks to me like it has.
The exhaust strategy you have will need the additional two fans on the bottom. The fans blowing on the radiator will reduce their effectiveness in creating air flow for your case. I would use them for exhaust. The other problem with having the lower fans be the exhaust, is that the air coming in from the front two, most-likely, will be pulled out and it may not get any additional temp benefits or even have temp increases base on the amount of hot air not being exhausted. If it can create a vortex of airflow, it may help in bringing the hot air out, but the higher the air temp, the more it rises. It would seem that the air would stay at the top of the case and continue to increase in temperature. Not sure until you get accurate temps of the various areas of the case. Most boards have a number of options for probes, as they are also fairly cheap to purchase, as I would also be curious of the board and internal temps of your case. If have those, that may tell you if the configuration is effective as you feel it is. With two 480mm radiators, you have enough heat dissipation for your configuration, but there is also the rest of the rig, such as the hard drives, DVD or CD, and the power supply, which all need to dissipate heat.
I would consider changing the entire set-up (maybe just a push/pull configuration change may be all that is necessary), but I feel that would be a bit of work and you may be resistant given your happiness with the current configuration. Check your internal temps, the temp of your board components not on a water block, the air inside your case, power supply, HHD, CD/DVD, etc. If those are good, then you are fine. If they are not, then a rework of the set-up may be warranted. Also if there is dust build up and dirt built up on the radiators, then this can be another reason, given the time and issues with removing and cleaning a radiator. Not that it cannot be done, but it a bit of work. If you like that, then that is a personal choice.
Sorry to be long wind, but I prefer to give too much information and all the options than short, limited statements, as I basically wrote a novel, but this is not a simple answer. The answer is a bit of personal preference, a bit of efficiency, a bit of airflow and finally the desired temperature of the components within the rig. Remember that this is not just the temp of the components which are included within your water loop that have blocks to dissipate the heat, but the overall rig and the things not actively on a block. I took a great deal of time and thought to work on mine, as I still have some issues with how it fits. I will change things a bit over the next few months, as I drain my loop I will reconfigure it with a purchase of a new top for my case allowing me more room for my push/pull top radiator configuration which will give me a bit more room for the tubing. Although the fit is not exactly what I wanted, the temps of my components within my water loops, dust build up and the overall temps of the components not in my loops, as well as the air temperature within the case are below what I expected.
We are here for assistance when necessary. Let me know if I or others can assist you in anyway. This only my opinion, as I am looking at nor have the intimacy with your set-up that you do. PM me if we need to have a conversation regarding this, as I would be more than willing to help in way you need.