I'm most interested in Pak43/KwK43 88mm gun and the D25-T 122 mm gun.

The numbers given on Wikipedia for the KWK43 are from Tom Jentz Book "Kingtiger heavy tank 1942-1945" and are correctly copied ( i checked ). Thats makes these numbers trustworthy i guess.

Tank gun performance is more than penetration and has to be seen in relation to the enemy armor, perferably to standart armor. Many German tank guns had far more penetration than neccessary for example while Allied tanks often were undergunned for some tanks but okish for things like the Panzer IV.

Jentz book has another table where both guns you mentioned are compared to each in other in their respective weapon system. ISII vs Panzer VIb

The IS 2 was unable to penetrate the front of the Kingtiger, who used the KWK43, at any range. It was able to penetrate the side on different areas but only on 1400m or less distance, which already is out of standart engagement range ( Range taken from Western Front at 900 yards might be higher on the Eastern Front). The rear was vunerable from 900m or less. The Kingtiger on the other hand was able to penetrate every part of the IS 2 over a distance of up to 3500m. Even the front should get penetrated over even unnormal combat ranges. BUT it is questionable if a weapon, to specifially deal with the Kingtiger, was even neccessary their numbers were low and German AFVs with such high armor were rare. Vehicles like the Kingtiger or the Jagdpanther or Jagdtiger ( frontarmor for both ) hardly justified the introduction of stronger guns because their numbers were too low. Afterwar reports from Normandy showed that front armor alone wasn't helping that much. If the strenght of the enemy front armor is known to the crews they will go for the side with good results. This disqualifies most German vehicles since most had only very strong front armor and leaves the Kingtiger and to some degree the Tiger as the only allround armored vehicles which would require very heavy penetrating weapons. The Panther for example had superb front armor but with sides exposed the Panther was as vunerable to the Sherman as the Sherman was to the Panther. As you see judging guns just on penetration doesn't help alot.

Edit: In regards to combat range i checked Zalogas "Armored Champion" and he gives the following percantages for combat range: 31,2 % Kill claims on 600-800, overall more than 50% of the kills were done over range of 600-1200m. A quick glance over the numbers confirms the 900 yard claim for the Eastern Front aswell.

The accuarcy of the KWK43 is often described as excellent but i have not come across a source which compares all major guns in terms of accuarcy, if books attempt such things, their methodology often gets questioned since they mostly work with wartime sources and different countries had different methods. They obviously didn't follow the same protocoll. What was the steal quality? How were moving targets described? What rounds were selected? Random rounds? What is a penetration?. Soviet sources on Soviet guns often give numbers for penetration and accuarcy which are questionable.

Edit: A book i recently read had some graphs for gun performance i try to find it.

While it's not exactly a study of their efficacy per se, there's a primary source US Army handbook floating around on the net titled German Explosive Ordnance (Projectiles and Projectile Fuzes) that would have all of the detailed technical specifications for every kind of shell fired from German guns. Perhaps comparing those raw specifications would be helpful for your research. One other thing to maybe keep in mind is that the quality of the material being shot at was very important - near the end of the war as I recall German tanks had very low quality armor material, which would skew the effective penetration of guns. Sorry I'm not more help.