The last few pounds, what gives???

Don't get stuck too much on just the numbers. When you picked the numbers 90+lbs ago you didn't necessarily have a real reference as to what they would truly mean!

You definitely look fantastic and, because of your activity level, if your intake is weighed and measured, I would definitely NOT go below your current 1700. Promoting excess adaptation does not seem to me to be a real advantage. And yes, adaptation DOES happen and is even more likely to happen as you've leaned out.

Furthermore, you are likely to hold on to some weight lifting generated water weight for as long as you're lifting. If you lay off weight lifting for a week you may lose that; but, I doubt that this would be a useful thing to do, other than satisfying you in terms of scale numbers!

If you weight yourself once a week it is harder to see subtle trends than when you weigh once a day. During the year I lost at almost 1lb a month there were several weeks and months where I would be higher at the end of an arbitrary time period than I was at the beginning even while losing at my steady almost 1lb a month overall. And that's without any hormonal fluctuations or intense exercise thrown into the mix!

Your diet breaks don't sound that long. A break would normally be defined as 2+ weeks.

Given that your health upside is much more directed towards protecting your large and fairly rapid loss, I would definitely suggest a maintenance mindset and playing with calories and food only with a view to maintenance and further loss as a happy bonus as opposed to a hard focus on additional weight loss.

You really don't want to create excess rebound preconditions by pushing for a hard deficit for marginal health benefits now that you're already leaner and at the tail end of a large loss.

AND, in any case, muscle building has a much higher chance of success with adequate calories as opposed to working through a hypocaloric regiment. 1700 net does not sound much for your 2+ hours of mucking around horses.

Overall, I would personally ignore the number you're at scale wise, switch MFP to 0.5lbs and INCREASE net calories, and carry on that way. Then continue to increase to maintenance level calories. And ignore anything other than a persistent and obvious weight trend increase that ought to signal the potential for a claw back as having overshot maintenance.

Again... your bread is buttered on the side of finding a way to maintain your amazing weight loss and continuing to being adequately fueled so as to meet and improve your exercise performance goals... not on hard dieting resulting in lower activity and further adaptation in order to see a lower scale number.

And, of course, decisions are not final. Whether you maintain now, or in five lbs, you will eventually have to figure out maintenance.

After maintaining for a year or two or three, you can revisit further losses if that's what you want to achieve at that point of time.

However, at this point of time it sounds as if you want to get stronger/more muscular (hence weight lifting) and I would assume you would also want to protect your weight loss.

Both of these will be more likely to be achieved by increasing calories at this point as opposed to decreasing.

Take care!