"Which one do you have and why did you choose that one?"
I have two 67's and three 17's.
I got tired of switching the saddles to bikes that didn't have a Brooks, so I kept buying them so that all the steeds are now well liveried. That's why. I have a large box full of failures - not all of them bad saddles, either. Some of them are plenty good for short rides of less than 40 miles, but some aren't. The more padded/gel, the worse for distance.
For a Sirrus with flat? bars, I'd go with a 17. At your size and weight, it should fit pretty good. You can measure your ischials by cutting off the four flaps of a corrugated card board box, stacking them, sitting on them for about twenty minutes while you watch the news or something. Then, measure the center to center dimples.
A 17 is 17cm across the seat portion. That's the extreme outside width. Be aware that there is a steel frame under the rear that curves around to the sides - right next to your ischial bones. You also have a fleshy pad surrounding you ischails that is about the size of a 50cent piece. All that needs to fit inside that frame, or you'll end up quite sore just to the outside of your sitbones.
So, when you get that dimple measurement, add about 1 full inch of width. That's your comfort zone. Now, subtract about 1 full inch off the width of the saddle, and see if your comfort zone fits inside. If so, it's golden.