I feel that the lifespan of the two should be pretty equal, even if you do over[B]speed[/B] the MKM 001 [overburning is a different thing ;)].
MKM 001 was supported up to 8x in some drives, and people still overspeed it to 6x and 8x [sometimes using the MKM 003 strategy] with few ill results. It can cope with 4x easily, and should be a sweet spot for you on both drives.
MKM 003 does fairly well up to 10x [and, in some specific cases, 12x] with burning quality. 4x is about the lowest you can go before you run into the territory of wasting time for no gain in quality [or a potential loss in quality]. Since the disc is designed for higher writing speeds, I’d experiment with 6x in the newer Samsung; it should be fine and shave a few minutes off the overall burn time.
General build & burn quality between the two is pretty similar, IMO. As long as you have more recent drives, MKM 003 is a worthwhile investment for use [and your drives should do fine with the MKM 003 disc model]. There’s really not much of a reason to specifically get MKM 001 over MKM 003 for you.
As far as deterioration, I haven’t heard too many reports of either disc model degrading horribly fast. There are a few reports of unreadable discs, but I haven’t had much of an issue with either degrading on me. These will definitely not last forever [every recordable disc has its strengths and weaknesses regarding longevity], but they should last long enough for us to recover the data stored on them and move on to the next big removable storage medium.