Well, according to wiki it could carry 1x 800kg bomb, 4x 250kg bombs, and I would assume it has a 100kg and 50kg option like the Ki-67 has.
It will climb better than most other bombers because it was very light. However, being a bit stubby and being an early war plane it was underpowered (part of the effort for super long range was to reduce weight, another was to put range over speed) and would make 260mph give or take top speed.
The question I would have is "what was a historically common bomb load?" -- because I don't know what these really carried very often. For example, 1000 lb bombs on P-51s were extremely rare, almost never happened. What would be "normal" for the Betty?
Interestingly enough, the Japanese never really sought to increase bomb loads like the Allies did. You can see a similar trend in the Ju88s and their predecessors. They seemed content with the payload, just wanted better performance. The Betty was only about 15mph faster than the Nell that it replaced, carried [roughly] the same bomb load [as any other Japanese bomber], had the same rear defensive guns (20mm dorsal instead of tail), actually had a hair's less range than the Nell, but overall it replaced the Nell. Surely it wasn't because the Betty was more survivable (they left the armor off of both!), so it really begs the question "Why?"
P.S. The above also suggests the Betty can easily stand in for the Nell (*cough*UntilWeGetTheNell*cough*)