A benchmarking framework was added 6 months ago in #6733, but there are still no (non-silly) benchmarks added to it.
Would be nice if someone added some benchmarks, so that it is easier to see that claimed performance improvements really are such. Some ideas (some easy, some more involved):

• Script validation (done in Add microbenchmarks to profile more code paths. #8873)
• CCoinsDBView caching
• Coins database
• Mempool (done in Add microbenchmarks to profile more code paths. #8873)
• EncodeBase58 performance see Improve EncodeBase58 performance #7656 (done in bench: Added base58 encoding/decoding benchmarks #8107)
• Wallet: Coin selection see Add index to wallet UTXO #7823 (done in Add microbenchmarks to profile more code paths. #8873)
• SHA256 throughput and other cryptographic hashes (done in bench: Add crypto hash benchmarks #8039)
• LockedMemoryPool random allocation/deallocation performance (when Locked memory manager #8753 merged)