Are you sure that 3.5F isn't a Xenotar?
I think the Xenar and Tessar are both great lenses. I shot quick tests (mostly to verify focus accuracy) with quite a few over the past year. All were good. Some were slightly better than others. No two performed exactly alike. None were as good as a Planar or Xenotar (particularly at larger apertures).
The Tessar on the Rolleiflex T does seem to be noticeably better than the older lenses (though prone to separation in the rear cell).