I have always SB'ed.....and then pin around the perimeter (particularly at the four corners) in an attempt to keep it square.
If its a biggish quilt (and lets face 60 x 60 is no lap quilt) I then run a line of large stitches vertically, horizontally through the centre lines (like in a cross) and then through the diagonals to hold things straight whilst I'm quilting, as the quilting goes in ... the stitches are easily pulled out.
Chose a colour totally unlike anything to do with the fabric or stitches ... I usually use an orange red ...which has proved priceless this time round as I am using an orange red backing fabric and have orange red blocks within the top
but its all good...there are loads of stops and starts in this piece of quilting so I am getting all those stray basting stitches as I go.
Don't know anything regarding SB and polyester wadding...Is there any info on the tin or the t'internet??