Here are my thoughts on the subject, whatever the're worth. First of all, niether camera has been out long enough to make an intelligent judgement about them. But I would say that the D-55IR uses the same technology as the D-40. If that's the case, I have always thought the pics from the D-40 were a little grainy. Now if that doesn't matter to you, then I would say go ahead since it is cheaper than the I-35ir. The I-35IR uses the same technology as the I-40 and I-60 which take excellent quality day and night photos. You may want to wait until a few of them get into the field to see if there are any common problems. Sometimes it's better to wait when new models come out just to see if there are any glitches.
Blessings.....Pastorjim