The 70-tonners are a bit lighter than the 44-tonner.
A little more finicky over the turnouts, too.
As for pulling power: mine pulls 5-6 40' boxcars around 9" flat curves ok.
I don't have the space for 10 cars on a straight
I haven't tried adding weight to the 70-tonner, but I don't see a whole lot of space to put it, anyway.
Two 44-tonners should be no problem.
And a single Kato NW2 could pull the horns off a bull.