No it is never silly to try anything

If I had something in my stash I wanted to use I would give it a go.
Make a tension square and see if you need to go up or down a needle size.
It sounds like it is one of those cottons that could be anywhere between a 5 and 8 ply so an 8ply might work well. Every knitter knits differently which is why checking your tension is a good idea. Together with one of my fellow knitters in my knitting group we are knitting the exact same pattern with the exact same wool, and to get the tension correct I have to use 4.5mm whereas she is using 5.5 and could have even used 6mm but she hates knitting on big needles.
let us know how you go,
Sharon
http://shazknit.blogspot.com