Thanks everyone. I'm quite sure whichever I pick will work out fine. It's very helpful to get insight from people with more experience than myself of course.
I was very much leaning towards the P25+ for the long exposures, bigger sensor and newer technology. But I'm a little less sure about the seller now. The P30 definetely has the edge being from a dealer.
Ken, you say the P30 isn't too bad with long exposures, I haven't found much information on this? I've looked around on Google but find mostly P30+ info. I don't imagine any of my exposures would stretch out into multiple minutes, 30 seconds would usually be the extent of it.