You don't want them to be too fat because there is a good chance they will slug out on you. A 1,700 gram firm female would be perfect for breeding as long as she hasn't lost any weight. Your snake needs to be healthy, not fat. You should be able to read your snake enough to know whether it's fat or if it has some fat stored up for breeding.

unhealthy fat=white between the scales, huge and squishy
healthy fat=firm maybe a tad squishy, and a little larger than average for that snake before bulking up for breeding season.