Boy, that's really a tight gauge for that yarn. If you have the yarn, knit a sample of the pattern to see if you get gauge, you might have to go down a size, but that would make it really dense. But at gauge, the sts would be about 48". It might be a little scrunched up, but you don't need 40" circs either. If you have to use a different size or find you don't like the gauge on either needle, you can easily use a 29 or 32" needle too. You can use that size to make smaller blankets or shawls or scarves knit the long way, but a 40" needle has just too much cord.
sue- knitting heretic