Hi
PK50 is faster and bouncier, less tacky, closer to a grippy ESN type rubber than a Tacky Chinese style rubber, throw is slightly higher than Tau 2.
I found PK50 was able to produce very high spin serves, spin levels of Tau 2 when serving was almost as high, but sort of less efficient, less serves produced the same level of spin as PK50.
Tau 2 seemed to be much more controlled, the ball went where I wanted it to!! less so with the PK50. looping with Tau 2 is good, PK50 the catapult kicks in and is sort of enhanced, less linear or predictable when compared to Tau 2, I made more errors looping with PK50, difficult to judge how much catapult effect there was going to be. balls went long more often!!
Sponge hardness of PK50 is softer than Tau 2, from memory PK50 is around 50 degree hardness, personally I find springy sponges with 50+ degree hardness and grippy top sheet difficult to play with!! usually the tacky top sheets of 'Hybrid' characteristic rubbers compensate somewhat, but this, for me is not the case with PK50, Rakza Z with a harder bouncy sponge and slightly tackier top sheet is easier to play with than PK50 (for me). (Beware!! Rakza Z mounted on a fast inner ALC blade starts to show its true speed capabilities, I dread to think what PK50 would be like on that type of blade!!! I usually use slower all wood All / All+ / Off- type blades (except for Nittaku Acoustic inner, which plays slower than Viscaria.)
Personally, I would recommend to use Rakza Z over PK50 (regarding a rubber with a greater catapult effect than Tau 2). If i was given a choice of PK50/Rakza Z or Tau 2, I would choose Rakza Z or Tau 2!!!! playing with these 2 were easier and more enjoyable!!!!!. when I tested PK50 I was really looking forward to trying it out!!! shame I DIDN'T suit its playing characteristics!!!
That said, in the right hands,PK50 would be a good choice for many players!!!😀