Have to echo what others have already said. I've been on the Poudre a lot between 1' and 5' and the MFS one time at somewhere over 3'. From Boundary to probably Pistol/Indian Creek or so, they are very similar rivers - continuous, fast, and pretty tight in spots. Below Pistol/Indian Creek on the MFS, the similarities disappear. The river opens up, so you have a lot more room to move around, whereas the Poudre stays pretty tight and continuous. The biggest difference for me, though, is the size of the rapids lower in the MFS drainage. There's nothing like Weber, Rubber, etc., on the Poudre in terms of size and volume. Complexity, yes, probably moreso than the MFS, but def not size.
The other big factor is having no road next door in case things turn south on the MFS.
By the waterside I will lay my head.
Listen to the river sing sweet songs to rock my soul.