User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-34061653-20190112095306/@comment-33341107-20190120122729

B214 I wouldn't say that CxC or trinia were out of nowhere, trinia was a reslut of his mutation pieces which he got as a result of juggernaut drive and CxC is the power of juggernaut drive focused through one of his mutation pieces. The mutation pieces hes had since volume 6 IIRC and jugernaut drive is from the boosted gear, the only one of his power ups I would say was out of nowhere would be DxD G and that, unlike Kiba, had a decent reason for the jump, he recieved the power of infinity, infinity is what made him jump to HD class, thats entirely plausable since we've already seen Ophis give people power. Kiba made a jump from maou class speed to HD class speed with a non longinus sacred gear? Thats not even remotely as plausable as DxD.

Power class I presumably is made up of physical strength, speed and magic/demonic power, Sairaorg is more powerful than Rias despite having no demonic power. Kiba was able to compete with Bikou who in the Azazel cup is worth 5 pawns, in the Azazel cup maou class people cost 5 pawns like Saji or Midgardsormr so that shows his speed to be around maou class, also iirc Sona's pawn was faster than CxC Issei and her speed was compared to Kiba.

Fenrir was said to be HD class because of his strength and speed so speed clearly does play a role in the overall power of HD class beings, Vali being faster than Crom makes sense since his sacred gear gives him immense speed, even before he got DxD L he was faster than most and DxD is releasing the power of Albion, the power source of his sacred gear.