Ok.. i'm just jealous that this thread is getting more hits than my "grrr to catch a fish" - but i'm catch'n up
hahaha
Sounds wise to go to a lower size - even if the floor DOES hold - it's not worth the constant 'worry' of wondering.
I can feel for you tho. I built a garage that's about the size of my house - 40ft x 30ft. It has an 11ft high first floor and a 2nd floor as well. I wanted the first floor open - so I had to design it with steel beams.
The kicker is - i bought this huge thing for businss purposes - i use the 2nd floor for storage. I actually have steel shelving like you see at lowes that house things. I agnozied, talked with an engineer about lbs/inch and all as well. I ended up upgrading my beam size to like 14inches (when he said 12 would be enough).
To this day i STILL climb up there and look down the beams to see if they are stressed at all. Wonder if the 5-6 column of 2x4's are strong enough to hold all that weight. Wonder if the next hurrican that comes thru will make this top heavy bldg collapse. I have a 1968 mustang i'm restoring as well as a 2001 Honda. Do i dare put them in? LOL
All to say - I feel for ya bud! Best advice i'd give ya - go with what gives you peace of mind!!
Overkill the supports; spread the weight over as large a surface as you can; do the math and get professionals to double check; EXPERIMENT by putting weights on the floor (sand bags etc) and have someone jump up/down near it - while you go downstairs and measure off directly below it for how much give it makes; lower the size (as you have done); etc
Do what gives YOU peace of mind
It's like a woman, you can't ENJOY each other, if one of ya are worrying about something else