I need a recommendation for a lightweight sleeping bag with 40x90 dimensions suitable for 40-60 degree conditions. I don't want a mummy bag and I don't need a bag for colder temps. I seems that all the larger bags I find are all built for sub freezing temps.

Butler bag if you want the best.

Coleman or Wenzel large size bags should work. Their temp ratings are usually on the optimistic side so they should be fine in your temperature range.

Have you looked in to a quilt(poncho liner type) with a good sleep mat?