Go with the 67. With your ischials measuring 5.5", there is also the fleshy pad that surrounds them which adds another 1' to 1.5' of total width. That's about 170mm.
Brooks saddles have a steel frame under the rear of the saddle that looks like a horseshoe. It comes around to the sides and cannot be 'broken-in' by riding - unlike the leather top itself. The sitbones and those fleshy pads need to fit inside that frame or you won't be very comfortable after a few miles.
At 230mm wide, you can subtract about 40mm of actual useable area and conclude that the saddle web is 190mm. With your ischial width, you should fit right in with a little to spare at the sides.
Now, another issue with us Clydes/Athena's is the room between the upper thighs, where the saddle flair is felt. That is called the pinaforis muscle. If you have alot of muscle mass in that area, reducing the distance between your upper thighs, you may encounter some rubbing there. Sometimes it may feel a little like a cramp or charlie-horse. Another reason to go Brooks, because they are slick and thus help to reduce the chafing effect of synthetics. If the mass is flab, you won't have that much of a problem because flab doesn't compress like muscle. A small blessing.
Good luck