The color cast produced by the sensor is the same in both cases. However the technical quality of the algorithms used for removing that color cast is not necessarily the same. I've found Capture One has consistently outperformed any other program with it's LCC tool.
The fact that you'll need to do LCC/even-fielding/shading (it's called different things in different programs) means that you'll very likely be using either Phocus or Capture One. LightRoom nominally introduced a tool for this, but I don't think you'll find many people using it. Capture One has a robust and deep toolset that makes it the software of choice for a huge percentage of the high-end market (not just Phase One users, but also Canon, Sony, Nikon, etc). It's image quality for single-shot captures is also the best you'll find; better algorithms/math for extracting the most detail out of the raw file. Notably, while Capture One supports a large range of small format cameras, it does not support files from Hasselblad or other medium format makers; only Phase One files.
The P+ and IQ series are built like tanks and have no moving parts (e.g. no fans). Any camera can fail, but the durability and longevity of Phase One backs is very good. It's hard to find them now, but there was a series of videos where the P+ was frozen in dry ice, baked in an oven alongside a cake, placed under the wheels of a 2 ton truck, dropped from the roof of a car onto concrete (don't try that at home please), and shot out of the air from a high distance while riding a balloon – working perfectly afterward. Tech camera use often includes very cold weather, very hot weather and other extremes.
The ease of onboard battery should not be understated. Using an external battery (which you can also do on a P1) is more than a minor annoyance in many cases.
Every P1 back can also sync at any copal shutter speed without changing any menu option. If you're not buying a P1 make sure to check on the specific back you're purchasing as some backs require you to change an option in the menu to indicate if you're shooting faster or slower than 1/8th of a second, which is especially painful when bracketing.
But I'm biased (we sell Phase One, not Hasselblad), so by all means you should make your own evaluation.
If you're on a budget and long exposure matters to you the P45+ was one of the most popular backs ever for tech cameras users and should be even less than a P65+. Its max exposure time is one hour. It's true it's "only" 40mp, but with Capture One's really great demosaicing algorithms you'll find it holds its own very well.
Of course if you can stretch your budget an IQ260 or IQ150 would both be excellent tech camera backs. It's worth considering if it makes sense to save up for and hold off on your purchase a year or two longer, the combination of increased coins in the piggy bank and decreased price of one of those two backs might make a better choice long term. Both provide an hour long exposure capability and the IQ150 would provide CMOS live view and a retina grade LCD for image review.
