Good internal sump skimmer for 400 + gallons

[M3AN ONE]

I am looking for a good skimmer that can handle a 400 gallon plus tank. Dimensions really do not matter because my sump is 18 inch wide and my stand is 45 inch high and I have yet to Install baffles.
My tank is only 300 gallons but extra leeway can't hurt.
I was also told at my Lfs that the best place for a skimmer is in my return due to water turbulence any input on if that is correct?

 

[BL1]

I would go with one of these
Reef Octopus SUPER SRO 5000INT In-Sump Protein Skimmer - AquaCave.com
Reef Octopus Extreme XS 350 Protein Skimmer by CoralVue - AquaCave.com
I wouldn't put it in your return, the water fluctuates in that section which changes how well your skimmer operates. You always want your skimmer in a section with a constant water level. I always put mine in the first section coming from your DT.

 

[M3AN ONE]

Are MRC Mr 3 or Mr4 skimmers any good?

 

[M3AN ONE]

Are ASM G4 or 5 any good either?

 

[Northstar24]

This is for the Marineland 300 Deep Dimension system correct? If so, take a look at the Tunze DOC Skimmer 9430

 

[recliner]

I have my skimmer in the first chamber next to the input hose. I use a thick filter sock and my skimmer works perfect.
I think the worst place would be in the return section. You'd never get it dialed in