Shows how much of a lottery mixed with a Black Art, Broadband is
I've used AR7s on both my line and my sisters, each on a different exchange. Mine is a poor line which on a good day will just about sync at 2M and stay up all day unless it rains, whilst my sister's line will sync consistently around the 6M mark and stay up for two weeks or more come hell or high water.
I've also used a 2-Wire on my line which despite its reputation for rock solid stability, is at best no more stable than the AR7 and, at worst less so.
Like many people I've acquired a shed full of modems of different varieties as I've tried to wring good results out of a poor line.