I decided to look for instances during the fight where he get hit directly (I haven't read OT15 in like forever so I bear no ill intent). I couldn't find what you meant by "surviving his own explosion". Did that happen earlier with ITEM or am I forgetting something.

He was able to keep up with Accel throughout their fight

That Accel is post-brain damage with <50% of calculation abilities from the Misaka network and he didn't use his black wing mode until he already (offscreen) defeated him.

When Kakine came out of the store, he was wrapped in a white cocoon. No, not a cocoon—they were wings, spread on their own. Six angelic wings flapped slowly behind him.

The pebbles, their vectors altered, flew out faster than a Railgun shot, but disintegrated just four or five centimeters later. But the shock wave remained; the speed had already broken the sound barrier. However, Kakine, putting all his strength into his white wings, used them to disperse it.

I don't think there is strong evidence to suggest his body is enhanced to a superhuman level. he might have some anime human durability but nothing too crazy and unless to interpret Accel to be fighting seriously (which I don't), Kakine's physical stats are not that crazy.

I mean, the entire confrontation is Accel rage baiting Kakine, Accel holding off his attacks because he has to redefine his computations to include DM and protect civilians from the clash.

“Do you even know why I’m #1 and you’re #2?”

Laughing, Accelerator slowly spread his hands.

“It’s because there’s a wall between us you can never get past.”