I've been using Gerbing liners, gloves and socks.
And ther two channel controller so that I can keep top and bottom at different temperatures.
The liner has heated arms - and you do have your arms exposed on a GS - and as important it has a heated collar. Don't underestimate how jolly nice it is to have a warm neck when there's ice about.
The gloves are 100% waterproof and the elements run right down to the fingertips, but only on the back of the hand. Heated grips are OK until it gets very cold as few of us have ahnds that are so small that they wrap right round the grip, so most of us end up with cold fingertips and thumbs.
Their kit is well-made and carries a decent warranty. I had a problem with a glove that was caused by me. I e-mailed to see if I could have it repaired and within 20 mins I got a reply telling me to send both gloves back and that they'd replace them FOC. Result!