Resevoir, how big?

How big or small should a resevoir be for a watercooling system? Does it matter? Is bigger better?

if you're gonna use a submersed pump, then you need one big enough to hold the pump, plus you need a bit over the pump due to the fact that once you start it up(the first time), some of your reservoir will be drained to replace the air in the tubes with water.

as far as more water in reservoir or less...well...more water means it would take longer for your temps to top off under load, as well as taking longer for them to get back down to low point when idleing the cpu.

i personally used a 4x4x4 box i bought from home depot and it works great to submerge my danner mag 7 pump.

I am using a fairly large reservoir, about 2 liters/half gallon. The time it takes for your temps to come down isn't very long , 1 minute for my machine. I use an 80GPH submerged pump flowing through a 12 1/2" x 5 1/2" x 3/4" radiator with dual 120's drawing through it. My coolant completely cycles 2.6 times per minute through the system. (80GPH / 60 minutes / .5 gallons) Temps stabilize very quickly, and because I have good airflow through the radiator and the waterflow isn't too fast, the cooling system works rather well.

I am a firm believer in large reservoirs, although some here will advocate higher flowrates using inline pumps instead.

I was thinking of using a 1.5L res. My pump is rated at 210 gph and I have a 4"x11"X3/4" rad with 3X92mm 38 cfm fans. does this sound like a good enough setup?

Sounds good to me, what is the head height that that rating is at? You have to account for the height differential and look at the rating at the highest point in the system.

At 1' its rated at 230gph and 3' is 190gph my case is 20" tall and the pump is about 2" from the bottom so total rise is 18" so I would say that the rating would be about 210gph.