first...

what are you keeping in your tank right now?

this is very important as to how you want your sump to compliment your
tank.

is it fish only? reef + fish or strictly reef? if it is reef, what
kind of corals do you have? small stoney, large stoney, soft, clams
(not a coral i know). all these corals require different lighting
intensities as well as different lights. also, each like different
flow rates and patterns.

the over flow rated for 600gph is tricky because you want to run a
1000gph+ pump...even given adjustment for head pressure, unless you are
going straight up from a basement, because you may have excess return
from your pump...which may overwhelm your overflow and cause some sort
of flood...something i have experienced in one way or another over the
many years of keeping wet critters. i would also ditch the sponge
located within the overflow box...if it starts to clog and flow
decreases but your return flow remains the same...guess what? time to
get the wet/dry vac out and start suckin' up water from your
mini-flood.

600gph overflow would be the max i would consider for a 48g tank. it
is my opinion that anything more than 10x tank turnover from the sump
results in decreased efficiency of the sump components such as
skimmers, chillers, etc.

if your return pump is too powerful...instead of dialing it back with a
ball valve...you can T it off and have the excess flow go back into the
sump for a in-sump closed loop.

if you want more in tank flow/circulation...you may want to place some
powerheads or other circulating pumps in there.

as for mag and quiet one pumps...i have and use both for various
utilitarian tasks. here's the skinny on them...quiet ones are more
quiet and mag drives are more durable and the reverse is true for each
as well. you gotta make the choice.

it is somewhat of a mystery to me why you have a wet/dry and live rock
in the same tank. most people that have a wet/dry use them for
fish-only tanks. and if the fish only tanks dont have wet/dry...they
use live rock as their source of biological filtration. if it were my
tank, i would slowly (keyword: slowly) take the bioballs out as they
tend to trap a lot of detritus and are a headache to clean and just go
with live rock.

scwd...not a big fan of them. they are great for their price and
function but your return water needs to be debris free....sometimes
hard in an aquarium...otherwise a pebble may get caught in the gears
and jam the whole thing up. plus, as far as i know...the biggest size
is a 3/4" and i need at least a 1" to 1 1/2"

hope this brief description of your questions help a little.