I have an Antec 300 case which I've added an overclocked Intel 920 and now added 6 drives. I have the stock fan for the rear exhaust and top. I've added 1 fan to the front to pass air over the hard drives ( 1/2 of them ). I'm going to add another fan would it be best to put a 2nd fan to run air over ALL the hard drive or add a fan to the side of the case?
I also have the Antec 300 case and personally I opted to go for the two front intake fans. I've actually cut out the side panel fan (I'm not a fan of them tbh no pun intended!) to accomodate a side window mod which looks very nice if I do say so myself.
Here's a print-out of some of my temps from HWMonitor if you're interested. As you can see the HDDs stay very cool with the two intake fans at the front. However, I will add that I use onboard graphics since I don't use my system for gaming. I would imagine the side-panel fan may be useful for spot-cooling your GPU.
Hardware monitor ITE IT87
Temperature 0 28°C (82°F) [0x1C] (TMPIN0)
Temperature 1 34°C (93°F) [0x22] (TMPIN1)
Temperature 2 34°C (93°F) [0x22] (TMPIN2)
Hardware monitor AMD Athlon II X4 630
Temperature 0 27°C (79°F) [0xD4] (Core #0)
Temperature 1 27°C (79°F) [0xD4] (Core #1)
Temperature 3 26°C (79°F) [0xD3] (Core #3)
Temperature 2 26°C (79°F) [0xD3] (Core #2)
Hardware monitor MAXTOR STM3320613AS
Temperature 0 23°C (73°F) [0x17] (Assembly)
Temperature 2 23°C (73°F) [0x17] (Air Flow)