That doesn't help significantly, since you only save the final O(k) dereferences. The situation (small k) where it's practical to allocate a ring buffer like this is exactly the situation where it isn't useful.
Actually, you're right, it's the larger values of k where this might make a difference. If the list items are scattered in memory, the cost of the buffer increases very slowly with k compared to the cost of hitting those extra k/2 items.
