I've slightly modified a couple line in the code and made a new branch for our witnesses: https://github.com/BitSharesEurope/testnet/compare/testnet...BitSharesEurope:testnet-witnesses

So far, memory usage has been reduced drastically and a bunch of transactions have already went above 2,000 txs/sec with > 8,000 ops/sec.
You can see the stats in real-time here: http://stats.bitshares.eu/#test