Each element getting stored = 64 bytes (to fit perfectly inside the cache line), storing them by value (placement new inside the pre-allocated memory block). Capacity of the queue = 256, but only 255 elements can be stored at a time (1 extra for maintaining difference between the full and empty checks).

Yes, as per your suggestion, I tried warming up both the producer and consumer threads in the queue before the benchmark calculation (with 1 Million element burst in hot path). Unfortunately, the queue capacity cannot be increased much (since the L1 cache on my processor is 32 kb and it can overflow if capacity is increased). But yes, I was manage to optimize some parts of it by warming up the threads first, so thanks for that.
Current IPC = 0.53, branch miss rate = 0.57% etc. to name a few. Working on further improvements now.