Which pump?
 

Mag 350
http://www.jlaquatics.com/cgi-bin/sh...logno=wp-mag03
or
Quiet One 3000
http://www.jlaquatics.com/cgi-bin/sh...logno=wp-q3000

I have an external setup and i'm guessing about 5-6 feet of tubing.
ps. I want to run the pump submersed.

For what I have heard... go with the Mag 350.
The quiet one seems to be not quiet at all, and give more often problems compared to the mag 350.

Submerged is OK for the noise, but your watertemps will rise. The pumps are about 70W
this will give you about 2 degrees extra temp, or you need an extra or larger rad. (depending on your setup) Making the pump "inline" will save you 1.5 degree.

This will be a high flow system, so I guess your blocks and rad are also high flow.

fhrost, this pump is rated as 40W watts, the 4000 one is about 50 W, so for a 10.5 ft pump, for me is a good deal.
http://www.aquaticeco.com/index.cfm/...etail/iid/7632