I got the 1250 from DDen w/ my maze 3 & 1/2" silicon tubing. The 1250 has a 1/2" OD exhaust and a 5/8" OD? inlet. Whatever it is, the 1/2" silicon works nicely w/ it. The water block has 1/2" fittings. The heater core and the brass fittings I used in my resevoir both have 5/8" fittings. (silicon is stretchy.) The brass fittings in the resevoir are 1/2" NPT (national pipe thread) on one end and 5/8" barbs on the other. The resevoir is made from 1" PVC w/ appropriate adapters, etc.
I put the rad down in front, and moved the HDs to where the PSU used to be, and moved the PSU up to the top of my Inwin Q500 full tower case.
The 1250 pump is large... it takes up two of my CDROM bays. The resevoir is easily the highest point in the system, and it bled the air from the line quickly.
The 1250 pump, like eheim pumps in general, is very quiet. It does, however, vibrate. With some effort, you can isolate these vibrations. I can barely tell it's running, w/ the rest of the PC turned off, and in a quiet room..
The 1048 would produce less vibration.
I tried changing the fittings in the pump, using a brass fitting that would have made connecting the pump to the resevoir very easy, but even w/ teflon tape, the fitting still caused leaks.. I'd only use Eheim brand fittings.
BOTTOM LINE: 1048 would be sufficient, but I chose the 1250. 1/2" all the way, baby. The 1048 has smaller fittings.. I think the exhaust is 3/8" and the inlet 1/2", but you'd better make sure.