In a future time in which most people have chosen to have a procedure to have implanted in their brains a network of filamentous circuits (described as looking something like a silver spiderweb woven through the brain, if you could see it with x-ray vision) that give them remarkable intellectual processing efficiency, recall, etc. (even conscious control over normally involuntary functions, like raising skin temperature in one's hand to blister-forming levels), the main character is one of the remaining people that have held out and not gotten themselves "optimized" (or some similar term). It's hard for the remaining unmodified people to compete, intellectually.
He is sought out by a woman who pitches to him, on behalf of the implant company employing her, a chance to try out a helmet device they've developed that can (through something like transcranial magnetic stimulation and encephalography) temporarily give one the experience of being optimized, so that people can take a test drive. They want the reaction of some holdouts before the company goes through with actually bringing it to market.
I think he may have slept on the offer. At his apartment, as ever, there's a very, very faint smell, of lilacs or something, of which no matter how much he scrubs, he can never quite rid the home.
I think there's some mention of him visiting or passing by a church in his neighborhood. It struggles to get more than a handful of parishioners, in recent years.
It emerges that a few years before, he had had a wife. In the hours after she had gotten an implant net, she had started reevaluating her outlooks on a variety of topics -- the story has a passage something like "By 1 PM she realized she didn't want her lifelong career; by 2 PM she realized she didn't need God; by 3 PM she realized she didn't need me." In some sort of black-out rage, he had murdered her. Rather than imposing imprisonment on him, the legal system had found him to have a previously unrecognized psychiatric imbalance that made him prone to impulsive fits of rage, and following some surgical or chemical correction, he was free, except for having to attend periodic mandatory therapy to help keep him balanced. (I think the short story actually starts out with him, for the first paragraph or two, attending some loveless sex session with some strangers, that is actually part of his legally ordered therapy regimen.) The aforementioned very faint lilac odor (or maybe it was some other scent) that persistently lingers (at least to his perception -- presumably it could be an illusory "Out, out damn spot!" Lady Macbeth situation, following the Othello-ish crime) in the apartment is from the soap she always used.
He takes up the offer and tries on the preview device. He starts thinking thrillingly efficiently in various ways. But when it's removed, he feels horrified at some of the chillingly cynical directions his thoughts had taken, and wonders with bitter regret what his wife would have decided, had she been able to try it.
I read this in the late '90s or early '00s, probably in Analog, Asimov's, or F&SF.