Ethereum is fundamentally limited by single threaded performance of a CPU. Discussion over GAS costs/etc is misleading because the maximum GAS that an individual node can process is limited and there is relatively little room to optimize execution.Early test networks reached 25 tx/second. With optimizations they may be able to reach 50 tx/second. Ethereum scalability improvements (PoS and Sharding) up to 30,000 tc/second.
Thanks for the comment! I saw testnet results and was impressed, but sharding test results are yet to be released so I'm waiting to see how it goes regarding txs!