Isn't it ? Anyway, they're top stuff, the numbers OP mentioned were way off actual capabilities so like others I think there is something else going on here.
Very doubtful it's hardware related.
Larger SSDs are frequently faster than smaller ones. That is part of what made me start this thread, I was wondering whether the 256GB SSDs in the 2016 MBPs were just that much slower. From the responses received it appears they are slightly slower but nowhere near as slow as the in-store demo machines I saw.
Yes the 512GB in the 13" is slower than the 512GB in the 15". It says up to 2.1GB/s write for the 13" and 2.2GB/s write for the 15". This would translate to noticeable numbers in the speed test (but probably not in daily use)
My 2016 non touch bar 13" base with 256gb: http://imgur.com/rde9M8A
Write speed slightly decreased while taking the screenshot, it goes upto about 1390MB/s
Unless you need that extra space, it is not worth buying the larger drive just for the speed boost. In day to day usage, you would never notice the difference.
Now if you are making the next Pixar movie on there and the speed bump cuts down video copy times by a 30% or so... maybe.