IMO it is something like
I really think the Borg/Lendl forehands were analogous to the forehands of Nadal/Federer. Borg with great accuracy, placement and consistency while Lendl with the power and clutch. Certainly both, especially Borg's forehand, was ahead of their time. Sampras had a tremendous forehand, but I mean hard to really rate considering playing from the baseline wasn't his biggest strength unlike the others.
I mainly agree with you in the top 3. I don't agree with Nadal /Borg as all time great forehands.
My top 5 are:
As I mentioned before there are/were some extraordinary forehands that produce amazing results at their times like Borg/Vilas (they heavy topspin ones were revolutionary on the 70ties), Clerc , Perez-Roldan (on clay), Mancini, Engvist, Bruguera(on clay), Roddick and Nadal.
Enqvist, Clerc for the reasons mentioned before.
I'm not sure if I am forgetting an another one worth to be mentioned.