You should look further "up" in the Walther section - in the sticky area. There is already a detailed post about all the trigger styles - here ya go
Walther P99 Trigger Systems
I think that will answer any questions U have about the triggers...
As for the 9mm vs 40 cal recoil debate - I will say that while I am a super, huge P99 fan (everyone here knows that I am), I think the P99 is best in 9mm. I have fired the P99 in 40 cal, and I would not like the gun nearly as much if I had a 40 cal P99. The 9mm version is already a bit snappier than most other 9mms. I'm not a wimp who can't handle the 40 cal recoil, but it is quite a bit more than the 9mm. And, not my preference.
There are always some 40 cal P99 fans that will pop up and countermand me. But, I will say that over the years on many gun forums, I have seen numerous people complain about the recoil on the 40 cal P99 - and they regretted getting the P99 in that caliber (wiching that theyw ould have gotten one in 9mm). The next post below mine may tell you how wonderful the gun is in 40 cal - and that's fine. All of this is subjective. But, I wouldn't want one in 40 cal personally.
And, as for the PX4 - I have said several times that while I have no interest in getting into the 40 cal round (I think effective shot placement with a 9mm is just as effective), IF I did want a 40 cal handgun, the PX4 would be the one to get. In 9mm, I didn't find much difference in recoil with the rotating barrel. But with the 40 cal, I looked at the gun after the first shot to make sure I wasn't shooting a 9mm. And, this was after I loaded the magazine with 40 cal bullets myself.
The P99 is and always will be my fav handgun. There be more accurate guns like 1911s and such - but in my hands, the gun shoots better for me than even a 1911. But, I only want it in 9mm.
If I were to go buy a 40 cal gun tomorrow, I'd get a PX4.
Your milage may vary, and you will get all sorts of opinions from others who respond after my message...