I have never had a heat shield since the rebuild, 3 years ago. I have driven it hard and worked it hard off road at low speeds. My bonnet has never gotten evenly remotely warm. I worried about it for a good while and used to deliberately get the turbo hot (4th up hill accelerating hard etc) then immediately pull over and check. I could barely discern any difference. When the bonnet is wet after rain etc it doesn’t dry any faster above the turbo either.
3 years later and the paint on the bonnet is utterly unaffected and I don’t worry about it anymore.