I just read this and I disagree. Respectfully. It's why I fish a 5/8 oz jig instead of a 1/4 oz one. It doesn't fall any faster. Gravity pulls at the same speed no matter the weight. The bigger tube will displace more water and slow it down some but same size tube different weight will all fall the same speed. Why I fish the 5/8 oz is because it's heavier and easier to control in the wind. Fall rate to the bottom is the same if I make it the same profile.
Oh and I don't use salt in my tubes either. If I'm using a weight then what is the salt going to help me with ? It only weakens the plastic.
The way you are fishing a Tube is much different than I do, and with all due respect, in my waters you'd struggle to get bit. The water I fish is clear and the smallmouth are pressured, they see a lot of tubes so the lighter the weight the better, anything over 1/4oz and forget it. A tube rigged on a 1/4oz head will have a wider spiral on the fall than a 5/8oz head, and it is really noticeable as we see it just going up to a 3/8oz head. It is different if you are Texas rigging a bait and throwing it dirty water or fishing it in 30' of water, but then the look of the bait isn't as critical. A tube with no salt will need more weight to keep it down when fishing in current, I have tried the no salt approach looking for a bait with a little more buoyancy and it didn't pan out so well, again I'm fishing in water 12' and under, weight is extremely critical and when fishing with current and wind a tiny difference in weight can really make a difference. Last year I had a day in which me and my buddy were fishing a small rock hump in the middle of the river in 5' of water, both of use were using the same tubes, I had a 3/32oz head and he was using a 1/8oz head, I had 9 fish landed before he finally switched to the 3/32oz head and then he began catching fish, but again, this is where there is a lot of pressure and presentation have to be fine tuned and a 5/8oz weight isn't even in any boats when it comes to tubes. For largemouth I will often T-rig a 4" tube with a 1/2oz weight and pitch it to boat docks with brush piles and dead falls, it is a reaction strike and so it is about speed more than action but smallmouth don't play that game. I do understand what you are saying but the waters I fish you have to really make minute changes in color, rigging, and weights, a 1/32oz difference in jig head size can be the difference between a banner day and getting skunked and while salt does weaken the plastic, you won't get bit here without it.