Buy the pattern in the gauge you want rather than yarn to fit the pattern.

Gauge 4 -
http://www.ravelry.com/patterns/library/top-down-turtle-n...
Gauge 5 -
http://www.ravelry.com/patterns/library/top-down-turtle-n...
Gauge 5.5 -
http://www.ravelry.com/patterns/library/top-down-turtle-n...
Gauge 6 -
http://www.ravelry.com/patterns/library/top-down-turtle-n...

Create a beautiful Turtle Neck Sweater. Worked seamlessly from the top down with no sewing at all other than a few tail ends.

There are detailed photo instructions on:

Swatching in the round.

How to make a double-layered neck

Unusual method to create the purl stitch in the rib section giving fantastic ribbing results.

Japanese Short Rows and how to close a gap when switching back to the round.

Double Twisted Yarn Over - to create a lovely unobtrusive raglan seam.

How to have hole free underarms.

How to do a Sewn bind off.

Typical yarns for this gauge are: Worsted, Afghan, Aran.
Sizes: 12 months - 10 years with a 5” ease.