Full Siphon Drain size question?

[Reign1]

Getting the plumbing together for my 30" cube. I got the tank for a steal unfortunately it is not quite configured how I would have done it. Either way Aquarium has 1.5" and 1" hold drilled in overflow and has 2) 1/2" returns on bottom of aquarium ( I do not believe I will make a CL).. Sooo far I will run a RD X DC pump (900 gph) on two 1/2" returns and was initially was thinking of doing the 1.5" as a siphone and 1" E drain . However the pump will only really likely be pumping 700-800 gph soo was thinking of just making the 1" siphon and 1.5 as E drain. What do you think?
TIA
PS yes I have been using the search function on site lots of information on this..

 

[theMeat]

One inch siphon, 1 1/2 e drain is the way to go