I think everyone's a little different. Ten pounds would be way too much of a range for me, but it's obviously perfectly fine for others. Five pounds is typically as much as I might fluctuate over a normal cycle while maintaining, usually more like 3-4 pounds. I might have the oddball bigger fluctuation. But I'd be way too far gone if I used a 10 pound range.
I think it really helps to have a good idea of your pattern of fluctuation across your monthly cycle. For me at least, a 3 pound upward fluctuation on day 3 (normal) is an *entirely* different animal than 3 pound upward fluctuation at the end of my period (abnormal). Same thing with ovulation (a peak followed by a drop). If I'm high but within my "range" at a point where I'm normally at a low, that's trouble.