Well, you really shouldn't be trying to utilize a deep sand bed since the proper way to execute a DSB
is to not have anything on top of the sand that would compact it, i.e. live rock, corals. It would need to be just a sandbed with nothing on it and had a depth of 5" or deeper all around.
I would suggest keeping it to 2" or less. I've heard that keeping it anywhere between 3 inches and 5 inches could be problematic. I personally like the looks of keeping a thin shallow sandbed, around 1/2" or 1" at most.
And i agree with mdaniel, you can do amazing things with reactors these days.