I guess the question is - how many deer have you not been able to shoot because you have your S&B? If the answer is coming to over £1000 worth then maybe it is time to look around.
Of course if you just fancy another scope then that is a different matter. I too have an S&B 8X56, Of the scopes I've had the chance to look through and play with I'd rate glass quality like this:
1. Nickel
2. Zeiss
3. S&B and Swaro
Of course people, generally, buy scopes for reasons other than glass quality plus I've not looked through some of the latest Zeiss and suspect they might be another small step forward and perhaps even better than Nickel now.
My S&B is more than adequate for anything I've ever needed it for so much as I'd like a Nickel there is no actual advantage in terms of my shooting ability. If, however, I spend the £2k+ on paid days, leases, syndicates, trips to stalk etc. then that would make a big difference to my ability to shoot deer.