I worry about this too - when I first started going to a Slimming World group, my initial end target was 9 stone. This was based on my BMI and that apparently between 8 stone and 10 stone is my "healthy range" so 9 stone was right in the middle of that.
Now I have several goal dates to aim towards - my start date at University (5th Sept), my birthday (4th Oct) and more importantly, my graduation (2nd Nov). Thinking logically and safely I should be losing up to 2lb a week. So for me to lose 2lb, by the time my graduation roles around I would be about 9st 7lbs. Thinking about it, that would be a fine weight. Still 26lbs (1st 12lbs) lighter than I was in May!! But i've also thought I would continue my weightloss until Christmas....
Why? Because I tend to eat alot of xmas, who doesn't? Sweets, selection boxes, cakes, puddings, tins of Roses & Quality Streets, mince pies, xmas dinner mmmmmm *actually drooling!!* lol!
So thought I would instead try and lose another 7lb-14lb until about the 17th December (when Uni finishes) so that from xmas week until new years I could let myself enjoy food again. Though I will still have in my head "don't eat that, think of the syns" which i think is good - stop me overdosing on sweets lol!! And then I don't mind letting my weight fluctuate a little throughout the year because I'll still be quite far away from my initial target for it not to suddenly creep back up again!!
But I hope that i will be able to look in the mirror and say "okay, it's time to stop" - but are we ever happy with out bodies? I mean, I see the slimmest most beautifulest girls who say "i'm fat/my hips are too big/my thighs wobble" and think to myself "i would KILL for that figure/those thighs/etc". I think it's true, you can lose so much weight, but if you are still in ''fat mind'' then you won't really be able to appreciate it.
I think as long as you aren't doing damage to yourself and that you aren't putting yourself under pressure then go for a size 10... worse case scenario if you think you then look too skinny then you can have fun putting the weight back on hehe! good luck xx