Are they dramatically different in most cases? I would think that it would only be different in this case with strike bombers (light and medium bomber types) and heavy bombers really have a number of standard loads that you can just choose from. I might be wrong, but I thought that at least with regards to US heavy bombers the loads were pretty well defined by the bomb bay dimensions, not the maximum take-off weight.
Look at the historical use and go from there. No point in having Lancasters with loads for bouncing bombs, incendiaries or Grand Slam. Though the Grand Slam would make an interesting bunker buster. You may want to allow for a couple of loads - one long range one short - this is probably more of a fighter bomber thing though.
"I love the smell of anthracite in the morning...
It smells like - victory"
Bombers can be assumed to be based near enough to the front to carry standard loads. They are not travelling to Berlin from Cambridgeshire, unless you design a scenario like that, and then you can edit the loads in the scenario editor yourself if needed.