I think it's impossible to pinpoint the names when we don't know all the players. There are still unknown Holy Knights, for example, who could be as strong as Garling and Sommers or even stronger (since they're still young at the time)... they'll certainly face important characters down the line. Plus, you remembered another wildcard: Bogard. As he's apparently Garp's right-hand man, this guy has been hinted as a powerhouse since the East Blue Saga, but still haven't made it clear so far. There are the other Gorosei, who seemingly can be summoned at will by a single one of them. There's also Dragon, although I think that he looks really 'meh' in the flashback, maybe he was pre-skip Koby level at this point. In addition, there may be another admiral there (recently promoted Sengoku?), although it's highly unlikely.
Actually, my only "certain" matchups are Roger vs. Kaido (since Kaido has Roger in his top 5), Gaban vs. Sommers (hinted recently at Elbaf), WB vs. Garling (there's the scar thing and WB needs to face a powerful enemy -- on the losing side, so it's very likely that he got defeated in God Valley) and Roger/Garp vs. Xebec (hinted since the God Valley incident was first mentioned by Sengoku). You must take into consideration that the Rocks' versions of Newgate, Linlin and Kaido (and maybe Shiki too) aren't still in their primes, so it wouldn't be weird if Rayleigh and Gaban were stronger than them at the time (in any case, their portrayal has been huge so far, Rayleigh was even considered a legend on par with Whitebeard back during the preparations to the Marineford War).
Actually, my only "certain" matchups are Roger vs. Kaido (since Kaido has Roger in his top 5), Gaban vs. Sommers (hinted recently at Elbaf), WB vs. Garling (there's the scar thing and WB needs to face a powerful enemy -- on the losing side, so it's very likely that he got defeated in God Valley) and Roger/Garp vs. Xebec (hinted since the God Valley incident was first mentioned by Sengoku). You must take into consideration that the Rocks' versions of Newgate, Linlin and Kaido (and maybe Shiki too) aren't still in their primes, so it wouldn't be weird if Rayleigh and Gaban were stronger than them at the time (in any case, their portrayal has been huge so far, Rayleigh was even considered a legend on par with Whitebeard back during the preparations to the Marineford War).
I don’t think that this implies that Rayleigh is on par with Newgate, just that they're both very powerful.