I have been dreading cutting up my Lian case for over 8 months. In fact, I have more than a few posts asking the same questions you are right now because I didn't want unnecessary holes all over the place.
The first thing I did a few weeks after I got it was to replace the 3 ADDA fans (~32CFM) with some Enermax adjustables. I removed the adjustable part so they ran full speed all the time (~40CFM) and are definitely not much, if any, louder than the ADDAs were.
It helped, but it was so long ago, I couldn't give you an exact number. Check around for posts from me back in the day
I want to say it was 2-3C cooler switching to the 40CFM fans in the stock locations.
Fast forward to about a two weeks ago. I finally cut out a hole under the OEM rear exhaust fan location and placed the 4th 80mm Enermax fan that I had there as exhaust. Definitely no giant drop in case or CPU temps. That was definitely more negative than positive (in/out were equal + PSU out). At least I like to think the second exhaust is helping keep the vid card heat away from the proc
About a week ago, I decided on replacing the intakes with 50CFM fans to get on the positive side. Then I got to thinking about finally dressing it up a little with some light and scoured everywhere looking for a decent looking LED fan that flowed 50CFM and wasn't any louder than ~35dB. They're just not out there yet, but the YS Techs would fit the bill nicely if you didn't want LED fans.
I let the aesthetic thing get the better of me and yesterday, I replaced the two 40CFM intake fans with some CoolerMaster 4-LED, 32CFM fans. I knew it was going to be a mistake in terms of cooling, but I just had to know what they would look like lit up behind the grill
Case/CPU temps went up as expected.
After deciding that all of my case fans are quiet enough to not be a problem running more fans with fewer CFM each, I finally worked up the nerve to cut a hole in the side as an intake today to get back some of the intake CFM I lost with the LED fans. I placed one of the 40CFM Enermax fans in the side as an intake, a little towards the back and a tad lower than the HSF. OMG what a difference.
Even with the weaker intakes in front, the same HSF, same exhausts in the back, and same ambient temps for the last 2-3 weeks (21-22C), CPU temps are 2-3C lower *with the case closed* than they have been with the case open.
Back-to-back readings today @ 164FSB and 1.8Vc:
before the side intake, side open: 38C idle/43C load
before the side intake, side closed: 40C idle/45 load
after side intake, side closed (duh): 36C idle/40 load
All I can say is, I am kicking myself in the arse for not doing it sooner. No more listening to the loud HSF with the side wide open, I have my LED fans in front (I guess it's a plus
), and it's cooler to boot.
It worked so well, I just need to keep myself from installing a 2nd side intake under it and a top blowhole to balance it out. I want to at this point, but am afraid it can't any better and I'll just be adding fan noise.
BTW, HS+F = MCX4000/Tornado and this is as balanced in/out flow as it has ever been (104CFM in/~110 out including the PSU).
If I was going to do it again, based on what I've seen in my case, I would probably NOT add a second exhaust in the back under the stock one, but would add a 40-50CFM side intake over the HSF area and a 40-50CFM top blow hole to balance it out. Note that I haven't tried a top blow hole, but obviously the 2nd rear exhaust on it's own didn't do much...it's pretty much just balancing the CFM out of the case.