spsaddict the DE 250s would be fine IMO, assuming you are going to use 10k bulbs. On my 24" deep sps system I keep many clams and sps on the bottom, and even the croceas and maximas (most light loving clams) do well. I have almost no sandbed. The 10ks really bake, but I have a DE 20k over a softie/lps tank that provides nice unsupplemented color but much less intensity than the 10k ushios. I supplement the ushios with 3 VHO actinics and love the color combo. If you are a definate 20k/radium man go for the 400 SE bulbs...
There is debate over the strength of DE 250s compared to SE 400s, but my first hand experience is that the 250 DEs really bake and are a great lamp...
In other words as always... listen to Kip!
Johnny