Case pressure and fan questions

the antec 300 is a good case, but i would save up more, and get somthing more like this
http://www.scan.co.uk/products/coolermaster-cm-690-ii-a...
http://www.scan.co.uk/products/coolermaster-storm-scout...

i have the antec one and with most newer cases like the antec one the power supply on the bottom is the pull fan. some people flip the ps over so the fan is dumping air into the case. my antec one not only has fan mounts in the front but also has one on the bottom of the case as long as the ps not to larger. with mb sitting this way ------------- heat going to be heading up. so you would want two fans one flowing from left to right >-------------> one to dump the heat outside the case. with new atx cases the mb are sitting on there sides. so that you want a fan on the bottom of the case pulling cold air out and one on the top blowing hot air out. if the hard drive and ssd temps are warm then you would add a front fan to pull cold air over the drives.
the antec one case is ok but has a video card length of 10 inches. so a lot of long cards wont fit. the 300 is a old case as the hd bay is fixed and is pointing to the rear of the case the hard drives and the video cards are going to hit each other or the wires will. the white case is going to give you some extra room and some better cable management then the antec one.
other cases like the r200/r300 wont break the bank. it not air pressure in the case that your looking for is the cfm of the case fans the rpm range and the db of the fans. the dm is how loud the fan is when running..think of your old video card fan when it rev's up...can you sit next to a pc that sounds like an airplane??if your case has good airflow the mb should be able to spin the fans down or with a fan controllers you can dial down the rpm. (larger fans...slower rmp..but same cfm as a smaller fan. a lot of good new 140mm fans now are 17db or less at max rpm. cheap case fans will have cheap berrings and or fan speeds.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
cheap...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
better

Personally, I prefer to have a small positive pressure inside the case, so that any excess air flow is from inside to out, avoiding dust intake. But that is a HUGE debate and there are ardent believers on both sides. I strongly advocate having a dust filter on every intake. And that's where it gets tricky. The specs for any fan are based on NO restriction of air flow through the fan, but any dust filter does reduce air flow, and it gets worse as the filter gets dirty. So clean it regularly. But the result is you cannot figure out the net pressure balance just from fan specs.

By the way, pressure does NOT determine cooling. Don't let anybody tell you a positive pressure results in trapping more heat. The real big factor for heat removal is air FLOW rate. You need to move lots of air through your case. You also need to be sure that a major air flow stream goes over your hottest components. (Lots of air flowing straight through open space past no heat source does you no good.)

For most gaming rigs, the components (especially the CPU and graphics card) generate a lot of heat, and most gaming rigs have more than 2 fans - sometimes 4 or 5, depending on what you can fit in. A mix of intake and exhaust fans is normal to ensure good flow through the case. More than 2 case fans, however, can be a challenge for automatic fan speed control by the mobo, since most have only 1 or 2 SYS_FAN ports to plug a fan into. There have been many discussions of how to deal with these issues here, so look around for threads, including old ones.

If you haven't purchased the PSU already, then a good quality 500-550W PSU is sufficient for your build with good headroom for some OCing. The XFX Core 550W is a steal at <50 quid at Scan; you get it for less with free shipping at Amazon.