Don't be an idiot--I don't mean that offensively, just for your own safety. Organic peroxides are incredibly powerful and unstable. 100mg can blow your fingertips off. Not kidding. It is easily enough for critical mass, which means it can detonate. 250mg is not very smart, honestly. I wouldn't try making diethyl ether peroxide at all, personally. I have made other peroxides before, although in very small quantities, with appropriate safety equipment. You have to realize that I have the proper experience in handling these materials, so that's a far cry from screwing around with them in your backyard. There's another thread on peroxides floating around on the forums somewhere; you should read it because there's some discussion on the peroxides themselves, etc.
As for your Vdet question, it's related to the density of the material. If you can pack the material at a higher density, you can get a greater Vdet out of it. That's just based on experimental observation and explains why explosives that are loosely heaped don't explode with as great a velocity of detonation as those that are packed densely. (This is not the case for ammonium nitrate, but that is for different reasons). Anyway, if the structure allows you to get a more dense crystal packing in the crystal structure, then a pure single crystal will have a higher Vdet. Hope that answers your question.