It depends.
My Bacchetta, fully loaded, weighs 35 pounds. My DF weighs 19 pounds. Going up hills, the power to weight ratios have the final word.
Into headwinds, I go faster on the Bacchetta.
In stop and go riding, I go faster on my DF.
Cruising on the flat open roads, its a push, but I feel better on the bent.
As for the knees, you gotta keep the cadence up, especially on hills. It is not easy. Hill repeats or trainer spins help. I hate doing them.
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Momento mori, amor fati.