I have both a regular Chisos and a wide Chisos, and have a regular Sawatch as well. There is a noticeable difference in the wide version and the wide Chisos is my go to bag down to freezing and a bit lower.
My Sawatch is one of the earlier versions as I am sure yours is, and is a bit wider than the current models. I have found that with a wide sleeping pad it is very effective at eliminating drafts. I have a 24" wide down mat and a 20" wide down mat, and much prefer the wide pad with the Sawatch.
The wide versions are also wider on the legs and footbox which may be a cooler. I notice it in my Chisos but it may be more noticeable in a colder weather bag like the Sawatch.
After purchasing the wide Chisos I thought long and hard about replacing the Sawatch with the wide version, but with the wide pad it has worked good for me. If you have a narrower pad you might try a wider pad before a wider quilt and see if that works for you.