Errm, you can’t have both those. The reason WHY Chrome is such a memory hog is because of the per-process tabs, There is tonnes of stuff duplicated in memory.
Opera is already the best memory managed browser out there, it will use what is available to the best of it’s ability, and hand back when other apps need it. People confuse this behavior with bad memory management. If my machine has 3GB of memory, I want my browser to be as fast as possible by USING that memory rather than it being wasted, likewise if I have a quad core machine, I want all my cores busy rather than just one.