Yes if you have a final size of only 1" then 600gph should be about max. But.....under pressure or full syphon 1" can handle about 1000gph but that is risky without some sort of emergency drain.
If it were me I'd try (no I wouldn't, I'd do it) to split it to two drains into the wet dry. That would require you to modify the wet dry though.
To be honest I think you will be fine. If it's working good now I'd leave it alone. Maybe add a power head or wave maker if you really think you need it. You'll have to wait to see if you have enough filtration at your current level of setting once everyone is in for a bit. I'd guess yes. Like I said before wet dry are very efficient filters they destroy ammonia and nitrite. Wetdrys are kind of like a static k1 filter or maybe reverse is a better way to say it..... anyway high O2 contact and water constantly washing away weak bacteria so only the strongest is able to survive and stay on the media.
If there is room maybe throw a couple bags of some biomedia in the sump part like rings or lava rock or something.
