I have a 95 Jaguar XJR 4 litre supercharged, would I need to use upper cylinder lubricant? Iam worried about the valve seats?

Odd that you are worried about the valve seats. The engineers that designed that motor were not worried. Guess you read all the ads for products you don't need. You want to protect your motor? Get the oil and filter changed every 3,000 miles and don't wait until it's black. You should check the oil level every 1,000 miles and top up the oil level.

I'm worried about every Jaguar there is. Your valve seats should be OK unless you did something to damage them, such as running 500 miles flat out top speed non-stop.

unleaded was everywhere by 1994 it should be designed to run unleaded. For all the leaded cars I put unleaded in it took along time to burn the valves out the money I saved on lube would of paid to rebuild the head 3 times.