In my HW98 I've tried the Vortek and ARH kits. After shooting the stock rifle I ordered the PG4 and used the supplied grease. There was a problem with the cocking shoe, it felt like it was dragging even after applying moly. I ordered an ARH kit and this helped but didn't fix the issue. I degreased everything and used krytox. I polished the shoe contact surfaces with 400 grit sandpaper and this eliminated all friction.
The ARH UK kit is a little softer shooting but there was a slight buzz even with heavy tar. I used this kit with Krytox and a 10mm delrin short stroke spacer for faster lock time. This was a snappier shot cycle but I did not see a noticeable difference in accuracy.
I'm currently using a Vortek PG4 12FPE kit and Vortek seal. With ARH moly and tar the cycle is quick and quiet. It's not hold sensitive either. So far the cocking shoe issue has not come back but if it does I'll use krytox to see if that helps. Accuracy seems to be consistent with different weight pellets. The JSB Express 7.87, H&N FTT 8.64, and Norma FT Heavy 9.1 all perform well with this kit.