I second this request. I too am considering a TrackIR purchase and am wondering the same thing. I've already read some comparisons... but would always appreciate anything anyone else whose experienced 4 and/or 5 thinks.
Given what I've read, my own thoughts on how I'd be using it... (mostly MS flight... and maybe IL2), and the fact that TrackIR 4 + Alaska DLC is probably less then TrackIR 5 alone I am leaning toward the 4.
Thanks