Overflow confusion

I am going to build a sump pretty soon, and am looking at some overflow boxes. Now I have read that you need one that won't lose its siphon in a power outage, which of course makes perfect sense. So whats the biggest difference between these 2 overflows and which one, if either, would have a tendency to lose the siphon in a power outage? I like the "3 parts" overflow better because it looks like with that one the water level would be higher in the tank and it would be a better surface skimmer. It looks like it wouldn't lose its siphon either, with that compartment off to the side like that. But it says specifically that the one with the "free" bulkhead won't lose its siphon.......Also how many GPH should I be aiming for in a 46gal? I think the goal is to turn the tank over about 10x per hour right? So 500-600GPH should be sufficient, yes?

I like this one better...

http://www.aquatraders.com/index.asp?PageAction=VIEWPROD&ProdID=80

But this one specifically says "continuous siphon"

http://www.aquatraders.com/index.asp?PageAction=VIEWPROD&ProdID=78

 

I had the top one and it never lose siphon as long as water stayed in the U tube, if it didn't it was a pain to restart but you could easily mod it with some airline and a check valve. It looks the same size as I had on the 90 and it was suffecient, it will flow as fast as the return pump puts water back in as long as the return isn't outdoing the overflow.

 

I have the bottom unit, it also has never given me any problem.

I would say either of them would work well, the top one having the advantage of the strainer slots.

Mike

 

The bottom one is a clone of the CPR overflow which I have. You need to attach the airline tubing on top to a venturi powerhead or an aqualifter pump which you can buy from foster and smith or that fish place online. I like my overflow and even prefer it to a built in overflow because there is less chance of overflowing your sump because you can adjust the water level with the height adjustment.