Can you buy back years or has that stopped. Look at this option first.
I'm almost certain a fairly large slice of your income is taxed at the higher rate so therefore relief will be granted at the higher rate.
The pension scheme is probably based on a years worked basis so if you work to 65 you will get 27/80 plus 81/80 (I think) as a lump sum (3 years for every year worked)
Revenue allow you to fund up to 2/3 of you salary inclusive of lump sum.
Bear in mind that you may not work till 65
The schemes acturies will advise if you are overproviding but I would be very surprised if you are