A true comparison isn't possible, no.
Like I said...a scale or "something" ...since they are roughly the same stats and training histories, I would think that if they are on MG for MG doses, the better steroid would be pretty obvious, as there must be one of them making more gains than the other.
I mean...if you put one person on 50mgs/day of Drol and 50mgs/day of 'var, you'll see differences quickly enough. I'm sure they can gague the more effective steroid in their situation, even if it's subjective.
I mean...the simple answer is that Tbol will produce more weight gained, ceteris paribus.