I wasn't sure if the Display Pro had better light capturing ability - I was thinking it might be better due to the simple fact that it's newer. It's a reasonably cheap piece of kit to add on anyway. So would I just be using the i1Pro for spot capture and printer calibration? or are there monitors that the i1Pro would handle better?
The i1 Display Pro measures to lower light levels whereas the i1Pro has a slower sensor that is more susceptible to noise that makes it less than ideal for some of the monitors that are available nowadays. In general you'd use the i1Pro for spot/strip measurements and printer calibration and the i1DP for most of the day to day monitor calibrations you'd be doing. The i1DP has display data tables to assist with calibrating the more common display types (CCFL, LED, LCD, plasma) to pair it up with the colorimeter technology whereas a i1Pro wouldn't require this. There may be some displays that would benefit from using the i1Pro however I'd imagine an update would come out to make sure the i1DP supported it as well.