Your results seem pretty close to mine. The last 5-6 months got me about a 10% gain. Strangely I keep getting huge gains in my 5sec wattage numbers even tho I never sprint. 960w->1310w in 12 months. Wish my FTP went up like that.
You'll win a lot more races if you can keep your 5S number going in that direction. Imagine what might happen if you start targeting your sprinting in training? I'm envious.