Generally you should:
-1- test your system and record the results
-2- make a change
-3- retest and compare the results
I second that plus it would be a good first step to record your temperatures. This will help you decide in how to setup your fans so you can get adequate cooling as quietly as possible.
The front intake fan is not a critical component. But in a system with a possibly older hard drive and a discreet gpu (admitedly the Saphire Ultimate is a special case), I think it`s worth having one, even if it runs at a fairly low speed.
The Nexus RealSilent (1000 rpm) is still the reference fan in SPCR`s reviews. The SlipStreams are also nice but they don`t deal with restrictions as well as other fans. In a typical case of the core 2 era the Nexus could be a safer choice.
If you do manage to find the Skythe s-flex at a reasonable price they are excellent too. I`ve been using 3 of those for about 8 years and they have aged pretty gracefully. They compare favorably to the 2 year old Nexus fans I`m using in another build.
The Arctic Cooling F series pwm fans seem to be well regarded too. They have a built in Y splitter so you could do what Arbutus suggests. The new fan will work as an exhaust, slowing down at low loads along with the cpu fan. The Evercool would be used as an intake, being controlled by the m/b as usual. This is a very efficient way of controlling all your fans, not requiring any extra hardware or software. The drawback is that the exhaust fan won`t always speed up when the gpu heats up, and the gpu is very reliant on the exhaust fan for staying cool. So you should keep an eye on gpu temps in particular, if you go with this solution.