Jeeez what a tough choice. I have a 5980R, but I don’t wear it as it’s too bulky for my wrist. I presume it’s similar dimensions to the 5990. I also have a 5712/1a which is an absolute pleasure to wear; goes with everything, sits under a shirt cuff comfortably and even lets me know when it’s time to howl at the moon :-) One of my fav features on the 5712 is the power bar which is something the 5990 is lacking. It true it is a tough call, but I would say perhaps weight your decision on some practical features? If you’re traveler an occult two time zones then the 5990 could be a good fix.
