Who dies would be VERY lopsided:
Urban? The urban survival rate without infrastructure will be negligible. How many decent people in cities have or can find food and water to survive six months without electricity? How many of those can resist their charitable natures as neighbors starve and then defend what they have against starving ferals? After looting everything in the city, including each other, how many ferals can make it far enough from a city to find surviving soft targets with supplies? Those who make it out will be very dangerous but also very few in number.
Suburban? That will be mixed. It will depend on lifestyle and distance from the concentrations of predators. Guns, supplies, teamwork, and training will be a big factor. Even close to a city, a neighborhood with 20 families, all hunting buddies, will have fairly good odds. Even near a smaller city, a neighborhood full of commuting accountants who have no outdoor experience and think guns are scary will face a bleak but short future.
Rural? I imagine those in towns under 20,000 will have extremely high survival rates. They will get cold, miserable, and irritable, but they will (mostly) live. They will not be able to harvest all the food they grow, but they will still have more than they can eat. They may be camping in a tent inside their cold homes, to stay warm, but they will not freeze.
I don’t believe the 90% fatality number or anything close to that, but I imagine the true number will be bad enough.
Urban: Those ferals in the inner cites, now numbering in the millions, will be reduced to only several hundred thousands - all members of various gangs - so few, from so many. Off they go to see what food can be found in the Suburbs ...
Suburban: hunting buddies? Great! Until the local game is exhausted and they have to compete with the next town over ...
Rural: Fine, until the Suburbanites are forced to expand their hunting ranges as game grows ever more scarce under intense, unregulated hunting pressures ... then winter, a particularly harsh winter descends nationwide ...
I have read up on this subject for 20 years now.
The threat is real, and the 90% fatality rate (after a year is very plausible. First to go are any folks on insulin, followed by all other folks dependent on drugs, like blood thinners.
One bomb is enough to do massive damage to our infrastructure.
Regarding who is most at risk, I direct you to Travis McGee’s Civil War 2 Cube. It explains it.
Looking around at our fellow Americans, I see weak, entitled, non-resilient people for whom a messed up order at Starbucks is a life-changing event.
I plan on eating those people.
I already have the recipes.