1.) #16 wins for sure. Cell will eventually tire. #16 will not.
2.) SA13 is hard to gauge. Some people like to put him on a ridiculously high pedestal, but ultimately, he 'only' stomped a few Super Saiyans(pre-RoSaT) + Kamiccolo. #16 could have done the exact same thing, with just as little effort. Suffice to say, I tend to place him around #16-level... And two #16-level beings should be > one #16-level being.
It would break down like this, imo:
#16 = SA13 = Imperfect Cell(peak) >>> Kamiccolo = #17 > #18 > SSJ Vegeta(pre-RoSaT) ~/> SSJ Goku(pre-RoSaT) ~/> SSJ Trunks(pre-RoSaT)