I'm probably the wrong person to ask. I'm perfectly happy with recording a 2 1/2 hour program to a single disk. Even though I'm taking a resolution/bitrate hit, I consider the hassle of having to switch disks in the middle of a program far outweigh's the quality hit.
Let's face it, the technology that enables high quality video to be recorded to a single disk (i.e., dual layer disc pressing) will not be available to consumers anytime soon, and may likely be bypassed by HD recording to Blue Ray discs. I've lived with VHS quality archives for 20 years, so even a 2 MB/sec, 352x480 DVD-R recording far surpasses anything I've ever archived to VHS (or even S-VHS) and I'm perfectly happy with it. I don't even fret or lose sleep over whether I'm feeding the recorder with an S-video or Composite signal from my digital STB. They both look great and even a coax feed is acceptable if I have no other choice. (Don't get me wrong, even I consider EP mode barely watchable). I chose DVD recording not just because of recording quality but also because the medium provides other significant benefits vs. tape such as direct/random access, menus and titling information that facilitate archving, a convenient form factor, and, hopefully, longer lasting archives. In my opinion, archiving a single program to multiple disks detracts somewhat from the "convenience" of the medium.
Bottom line is that PQ is a subjective issue and only YOU can determine what minimum quality level is acceptable to you. This may take some experimentation on your part to see whether (1) the differences in quality are perceptible and (2) whether a perceptible quality hit makes a difference!