Probably one of those things I'd hate to give blanket advice to from hundreds of miles away to somebody with different soils and conditions, but- other than the thinnest timber soil "here", I think anything over 100k in 30" rows with a quality planter is just insurance.    I'm thinking about doing some strip trials down to 75 or 80k in fields that I have gotten very good patten tile in now.  Once the chances of problems with crusting, ponding, etc. have been mitigated my feeling is that saving some seed dollars and spending them instead on more potash, fungicide, or whatever
is likely to put more bushels in the truck.

"Here" provided the stand is established well and consistent, I don't see a noticeable difference between 30" and narrow row beans planted and sprayed same way same day.  But it's been a really long time since we had an acre of beans without a strong residual preemerge down.