iTunes "only sync checked items" method

I've got more in my library than will fit on my iPod mini, so I'm using the options that only synchronises the checked items. This has worked quite well so far - If I want to add say an album worth of music then I uncheck the equivalent volume of music so that the new songs will fit.

The problem I've got now is that I added a large volume of music to my library that is by default checked, and I've got no idea how much music I need to uncheck to make all the new stuff fit...

I keep unchecking a few albums worth at a time then trying to update the iPod, but I've still got too much to fit on. I've got no idea what volume of music I've got checked (only that it is still more than will fit on my iPod) so don't know how much to uncheck to allow it to synchronise the iPod - Is there any way to find out what volume of music in the library is checked?

Is it just easier to use the "Manually manage music" method?

Cheers!

I would suggest creating a playlist called mini or whatever you want and just dragging whatever you want on and off that playlist and having the mini just sync with that playlist