The 8+ is the middle pic - now the only pic (shows "8+" in quotes). When Pete at TWL first started making his power cables, the 8 (and then later the improved 8+) was designed as a heavier gauge PC that would work well on any component but specifically designed for amps - particularly for higher power/high-current demand amps. It didn't take long for Pete to move to the 7+ and then discontinue the 8+ since it was, in fact, quite similar to the 7+. Personally, I've found the 8+ worked great on all my amps including a McCormack DNA-500 amp and a NAD M2 integrated.
All of Pete's power cords are exceptional in that they all provide a detailed yet relaxed, highly musical presentation. Unless you have a truly monster amp or special power requirements, I think the 8+ would work wonderfully in any application.