As a user & owner of a 645D I usually don't use it beyond 200 iso & can tell you noise at either 200 iso or 100 iso is not a problem. I also own a Canon 5D MK II and it beats the pants off it as you'd expect. Files should be opened in PS or similar rather than a basic file viewer too.
Regrading camera availability for reviews I would be very surprised if DP Review had requested a camera from Pentax for enough time for a full review that Pentax would refuse such a request. I also purchased a full compliment of older Pentax 645 lenses for my 645D and have been very impressed with the quality of all of the earlier glass, have even been able to purchase a 645 mount Hartblei T/S lens which also gives great results. If possible DP Review should get hold of some of these earlier lenses as part of a full review.
Finally, some further testing on the 645D. I hope this means a full review soon. DP Review have been remiss not fully reviewing the 645D when it was first released. I own a 645D and love the IQ. It is slow to process images given the huge file size & Pentax should do something about thethering, but some of this can be forgiven given the IQ & price.