Seating for 8 ft. tables

They should fit, but I don't think they would have much elbow room though

Typically, an 8 foot table is set with 4 on each side. You can probably squeeze 5 in on a bench, but it might not be too comfortable. Can you seat people on the ends?

I wouldn’t seat more than 4 per side. Just because they can fit doesn’t mean they should.

Airline seats are 17-18" wide. If you put 5 people on each side of an 8' table, they each have about 19". Personally, I think that's way too close, especially on a bench; they won't be able to move their elbows to eat without bumping into the person next to them. The middle people are going to be completely squished and if they want to get up while others are sitting next to them? Forget it! They won't be able to do it unless everyone else moves. For a table of 10 little kids? Sure. But not adults. If you have even one person in 5 who is "plus-sized," they aren't all going to fit on a bench and that will be uncomfortable and embarrassing.

I would be super uncomfortable being that close. I'm not a particularly large person - i just hate having no personal space, especially when i'm eating.

I wouldn't do it. I also had 8 foot tables and had 4 people on each side. 5 would have been way too tight especially people of average size. See one of my pics below for reference with 4 average sized adults.

ETA: I just noticed you said you plan to use benches instead of chairs - this would be way too tight and uncomfortable with 5 people on one side. Honestly, it would be even with 4 people on one side because benches are so hard to get in and out of if you are in the middle, plus wearing a dress.

I also had 8ft rectangular tables and seated 4 on each side and one on each end, for a total of 10 guests. I was nervous it was gonna be tight but it turned out fine. However, seating 5 on each side, even with benches, seems like it would be way too tight.