The Apex kit comes with a radbox that allows for rear out of case mounting of the rad, this will render issues with case air running through the rad mostly moot. Yes, to retain use of the rear fan you'll have to modify the radbox to allow the fan to still push the air out and you'll get some of the case air pulled through the rad but not as much as if the rad was mounted in the case roof.
An alternative is to move the case exhaust fan to a blowhole in the roof of the case to allow the hot case air exit where it can't get sucked through the rad. It has the added benefit of getting the stale hot air that builds up above the PSU out of the case, always a good deal.
About your temps, you'll see a tighter group between idle and load, the idle will likely stay around the same but the load will be reduced by anywhere from 3-7*C as reported by the mobo, but, be aware that mobo reporting isn't the most accurate so it's good for an idea of what you've got, it can be anywhere from 5-10*C higher or lower. This is why so many of the watercooling big guns poo-poo testing using motherboard monitoring.
Your GPU will see a radical improvement in temps though, as much as 20-30*C reduction in load temps! This is of course assuming that you watercool the GPU...
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An alternative is to move the case exhaust fan to a blowhole in the roof of the case to allow the hot case air exit where it can't get sucked through the rad. It has the added benefit of getting the stale hot air that builds up above the PSU out of the case, always a good deal.
About your temps, you'll see a tighter group between idle and load, the idle will likely stay around the same but the load will be reduced by anywhere from 3-7*C as reported by the mobo, but, be aware that mobo reporting isn't the most accurate so it's good for an idea of what you've got, it can be anywhere from 5-10*C higher or lower. This is why so many of the watercooling big guns poo-poo testing using motherboard monitoring.
Your GPU will see a radical improvement in temps though, as much as 20-30*C reduction in load temps! This is of course assuming that you watercool the GPU...
pfft ...stick with air.