I have had several dom0s and done testing with just dd reading from the disk. I found that on dom0 I got a reasonable value that I associated with my expectations for the HW (80 MB/s, IIRC, and this was normal ATA disks 4-5 years ago). It was about 10% slower to read the backing file in the dom0 fs, and 10% slower again to read rxbd0a in the domU. It looks like you are getting 529MB/s read on the disks. This sounds hard to believe and I wonder if your test is big enough to get it out of the cache. With dom0 you'll have less memory and less cache. I don't understand the domU write speeds being so low.
Attachment:
pgpoyFJD52uQT.pgp
Description: PGP signature