Just so I am clear, you have not shot either a UMP or MP5 SD, but you plan on spending in the neighborhood of $3,000+ to buy one or have one built? If you have not shot either one, I would go to a rental range and try them in semi. Usually if there is a model I wish to try, I search for a used one, at a good price. If I like it, I'll keep it. If I don't, I'll sell it for what I paid. But especially with the extra tax stamp for the can and all the waiting just to try it, the SD will take forever until you could try it. If you don't like the SD, the loss on the extra stamp for the can to be sold out of state would make it that you'd have to get one heck of a deal on the SD to break even on the resale of the SD.
To me your question is so subjective. Especially since there is a can thrown into the decision. I have no idea as to how you perceive sound, what your size and weight are. Even if we where of the same height and build, how something feels, weighs, or sounds like, could still be totally different than it would be to me. Now as far as versatility, the UMP can be shot in 9mm, .40 S&W and .45 ACP., suppressed or unsuppressed. The SD is a "one trick pony". But what a cool trick the SD has.
The biggest thing I didn't like about the UMP is it is blow back. I have found, the more mass moving around inside a gun, compared to the total weight of the gun, the more the gun moves around per shot. The greater the movement of the gun, the slower follow up shots are for me. It is my understanding that the UMP replaced the MP5 series simply because the UMP was much cheaper to produce, but could be sold for about the same money. Therefore, higher profit margin for HK with the UMP with the benefit of being more modular. Could the MP5 have been "updated" in this way? I'm sure that the MP5 series could have been adapted to a modular steel/polymer receiver, but would have cost more money to adapt the roller locked function to the new style of manufacture than simply make the gun with a blow back mechanism. But HK management at the time was looking for profit.
So go to a rental range and try a UMP and MP5 SD. Even then, you aren't going to be able to try the SD without hearing protection with other shooters using unsuppressed firearms around you. I live in NH and waiting on an orientation class to join Pelham Fish & Game. So you wouldn't be able to shoot one of my SD's after March. By the same token I don't own a UMP clone, nor am I interested in buying one. To me the UMP is a step backward, but there are others here that love their UMP clones. My first SD was a Coharie Arms that I bought for $1,450 including the can when Todd had his "Going Out Of Roller Locked Guns" sale. I replaced the MIMs bolt with a RCM bolt and I had the can "upgraded" by RCM. The Original CA can had all stainless steel internals and weighed over two pounds. That made the gun very "muzzle heavy" to me. RCM replaced the internals with anodized aluminum and shaved over one and a half pounds off the weight of the can. All told I have just over $2,000 in it including the tax stamp. So even if I didn't want it, I could have sold it for what I had in it. YMMV.
Scott
