There's an alternative method of calculating ideal weights by looking at body fat percentages, rather than just BMI. I quite like that as I get much higher (i.e. for me more realistic) figure doing that than I do using BMI.
Calculating it that way I would need to get down to about 18% body fat (and that's assuming no increase in muscle, so possibly less than that) to even get to the top end of the supposedly healthy BMI range. The healthy range of body fat for my age is 23-33%, so I will probably end up at some point being technically overweight, but underfat - if that makes sense?