If the choices are between a fast and a slow weapon in your mh, all else equal, the spreadsheet is probably correct in suggesting lungbreaker mh. If anything a rib spreader offhand might make more sense, but it's apparently not suggesting that. The only downside to lungbreaker is that it is more poorly itemized for mut, but the yellow socket may make up some of that ground.
I understand that you're saying the different tools are giving you largely different results for which weapon should be in your mh, but the actual projected dps change from switching to one or the other isn't actually that large is it? I would suggest sticking with a lungbreaker; most previous BiS lists had it in the mh with either another in the offhand or a heartpierce/rib spreader there instead.
May I also suggest updating your profile to reflect that you moved to Frostwolf so that people don't have to guess at which Jeanyes you are.
