I play with the RF97A, and ime, I agree it has a specific stiff feeling, but I would def not call it a stiff racket along the line of the Graphene Speed Pro or Prestige Pro (which I own/ed). Fwiw, I find the IG Prestige Pro (which I own), a much stiffer playing racket, much in part to the harshness outside of the sweet spot.
I find the 6.1 95 the only racket that ressembles the RF97A.
Imo, none of the Head models are similar. Even the Graphene Prestige Pro and the PS97 have little in common.
I felt the same way about the IGPP. It was a stiff, boardy feeling frame to me. Didn't particularly enjoy it.