I have never knitted a hat before and decided to start with the "Simple Hat with Ribbed Edge" from this site, actually (http://www.knittinghelp.com/knitting...opic.php?t=123). The only problem is I don't have size 7 needles. How different would it be if I used size 5 or 6? Would I have to change the number of stitches?
Why not knit a swatch? Cast on with your size 6s, and see what your gauge is... you might not have to make any changes at all! Usually the pattern gives a gauge with "suggested" needles... you might get that same gauge with a different size needle. The gauge is more important than the needles, for sure!