Reading the excellent "Through the Aegis", I noticed something.
Serf's Parma, but there's an effect (I believe it is called Zeus's Crate) using a boosted version of the Unseen Porter (ReTe base 3), with +2 magnitude for size.
It can lift 100 tons.
Thus, logically speaking, without the extra magnitudes, we could assume that The Unseen Porter, and thus a +5 Str character, could lift about 1 ton.
Now, I have no real problem with Str + 05 allowing one to lift great weights.
First, we're outside the "normal" range of human stats (-3/+3) on a system that, quite often, isn't linear
Second, this is mythic europe, with the same book having a magus who claims to be a reincarnated Heracles, son of zeus (with a club and guardian to somewhat back his claims) at Str +05, the maximum strength for non-giant-sized people. This is the level I picture Hercules (tv series), Clash of the Titans, or Captain America (which, IMO, fills the mold for +5 physical stats), all "mythic" characters.
Third, since strength increases by 2 for each +1 size, +05 is what we could expect from the smaller giants (stronger size +2 or weaker size +3, with a weight from 465 to 2150 lbs), which I can picture lifting great weights.
Now, this still seems a little big
But, since tUP gets slower as it lifts more weight, I think we could safely assume that the crate does the same, trading speed for weight, and thus cut everything by 2, which would give us a lifting capacity of about 0,5 tons for a +05 strength character, which seems more reasonable, albeit still mythic.
Thoughts? Comments? Tomatoes?