Jason ,the problem is that ,there really isn't any good DE bulb selection for 400W.
I am not sure if you are using a hood or retrofit however the ICE CAP DE pendents ,are the only ones that can be used both for 250W & 400w,this way you have the option.
Also for you current set up,if you need more PAR ,what I recomend is the
AQUACONNECT 250W 14K DE,using the ballasts you have they will have the same color of GEISMANN 20K DE & will have twice as much par.
We just imported these bulbs & they are already @ some stores ,in BC you can buy them from Hidden Reef & Alberta Golds.
I hope this helps