Yarn Question.....

[LoriSax]

I have the pattern for the Stella sweater from Berroco. It is a lace pattern. The pattern calls for Smart Cotton Yarn by Berroco. It says to use size 7 needles. The gauge is 20sts=4". I would like to use a different yarn that I have, and I do not know if it is suitable. It is Linen Isle, 50% cotton, 30% Rayon, and 20% linen. It says to use size 6 needles, and 5 sts=1 inch. If this is not suitable, can you think of something off hsand that is, that I can just get at the store instead of my LYS?? I am shopping on a budget right now. THANK YOU!!!!!!
Lori