I expect what GP meant is the default TCP window size, so in a situation where bandwidth costs are dwarfed by roundtrip costs, these two cases will end up taking essentially the same time, because they will incur the same number of ACK roundtrips. Don’t know if the numbers work out, but they at least sound plausible.
No, there is no way the numbers would work out to the same number of roundtrips. The sizes are different by a factor of 2.5x, and the congestion window will only double in a single roundtrip. The only way the number of roundtrips would be the same is if both transfers fit in the initial congestion window.
