Please help me choose a scope. This is going on my factory Mark V 257wby. The Z5 5-25x50 is only $1600 and goes to 25x magnification. However, I don't want to regret not getting the better scope. Does the Z6 have better glass? I don't know if I will ever use anything over 18x so the Z6 may be better. The Z6 is about $2250. How can I choose?