I have been accused of OVERKILL many times before in my life
I still live by the old rule:
If more is better, then too much is just right.
Honestly, my thoughts were to make the Res as large as possible, more water = cooler temps even if the system sucked ( takes longer to heat more water) this theory was proven with the first W/C I installed. The Ice burg system. After Res broke I built a new one out of Plexi making it as big as I could and still fit it into case. End result was a 1 degree C drop in temp. Mind you I was only able to increase the volume to about 1 quart but it did yield a lower temp.
Second reason, If I make the res the full hieght of the tower, combined with the small outlet area on the opposite side of the Res, the chances of air bubbles making their way back to the pump are Slim to none, Thus faster bleed time.
As it sits I can totaly bleed the W/C box in less than 5 minutes,
Fill it up. lay it on its side for abot 30 sec. stand it up then lay it on its other side fo another 30 seconds. Close off one PC feed for about 30 seconds, open it up and close off other PC valve for another 30 seconds. Open valve again and you are done.
Hope this helps
Aardil