I'm trying to remember the name of a sci fi short story I read back in the 80's or 90's. The story could have been based in the 50's, 60's or 70's. The main character of the story was a bank cashier, a not too smart man that wasn't particularly good at his job. He had trouble with numbers and would give wrong change etc.
Somehow he received some sort of brain implant or computer augmentation. It wasn't via surgery and I seem to recall it may have been via some other dimensional being? The device may have been called an "X-" something or other and may have been a prototype but I'm stretching here and I could be wrong. A side affect of the implant/computer was blinding headaches until he reaches some sort of evolutionary plateau.
He got better at his job was promoted to higher positions etc.
In the course of this it seemed he was becoming almost a God and I remember him evolving or altering a woman to join him. There was his concept of beauty which evolved with him and previously beautiful women were seen as coarse. Mention was made of the size of the pores on their skin.
There was some twist at the end with the female.