I appreciate your advice.
My bike is '11 CannondaleCaad8-6, size 56, and I'm 5'11" in height.
Caad8 is a rec easy rider, with handlebars about 1.5" below the seat. Toptube length is normal, but stem is close to 4", a little more than what I've used in 4 previous road bikes.
I"m 63 years old. Have tons of shoulder injuries in the past. My triceps hurt until I start riding later in the season, like more than once every 2 weeks.
Neck, my bad. I surfed shortboards for 25 years, and 20 years ago, after I stopped surfing, I already had neck problems.
Butt. Stock seat, slight recess in the middle, fine if I ride more than once every 2 weeks.
G/f is an ex Cat111 rider (7 years ago), who can still ride metric centuries in under 4 hours, training once a week for 40 miles. Me, I ain't riding on no rainy day with 30 mph crosswinds.