1. Hard to say when all we know is that he surpassed Kami and it seems a bit of a stretch to assume Kami's training made up about 90% of their gains or something, at least for Tenshinhan and Chaozu who could spar together. At most, I'd say Chaozu beats Weighted Goku, but would lose to his unweighted self either purely or partially due to the Kamehameha.
2. Probably Tenshinhan. Even assuming he made great gains in those 6 months, I'd still say it was the more beneficial portion of their training and Yajirobe likely wouldn't improve as much as the others due to laziness, his 970 rating setting a decent benchline for Tenshinhan. On top of that, Tenshinhan has far more techniques to help him get the upper hand.