Roy, I did some further research, and according to the Smithsonian Magazine the Arado 234 had a top speed of 456 mph. According to the Air Force Magazine the Me 262 had a top speed of 547 mph. As you say, there are different versions of the aircraft specifications, but the Smithsonian is a respected institution, as is the Air Force Magazine. I have watched several Mark Felton videos on YouTube, and found them both interesting and informative. I guess we may never know for sure, but one thing is certain, for their time, both aircraft were extremely fast.
Peter.