I think that you would know since you have actually ran them before. I ran a pair of 2" small peerless and CDT speakers that way and they were nice, but one set was poly with an aluminum dust cap and one set was treated paper.
I was contemplating running either the PPI or the SoundStream set in my Lexus. I was going to run the mid in the door and the 2.5" and tweeter in the stock location on the dash, which is not a huge obstacle. I would have to fabricate a bracket because the factory sound system is configured with just a tweeter there. The Mark Levinson system has a mid and a tweeter on the dash so there is room there.
I opted to try a two-way system with the mid in the door and the tweeter in the dash location. My factory system also has a center channel in the dash so I will have to work to blend it in and try to get the best stereo separation and center image that I can. I think that I am like you in that I like to try to keep it as simple as possible.
Are you still liking your Boston SPZ's??? I ran the Boston Pro Series back in the early 90's in a competition car and I absolutely loved them. I also was running all SoundStream DII series amplifiers. I had a center channel in my car in 1990 using a Boston Pro 4.2 set with an Audio Control ESP-3. It was a lot of work removing the entire dash and fabricating brackets and etc... but it was well worth it in the end. I am going to run a Polk MM6501 set in this car just because I want to try something different.