Operas caching system has also undergone a major rewrite. A nice feature in the new cache system is opera:cache, which allows you to browse through everything that Opera has stored on memory or disk. But the new cache system is most importantly much faster. You should definitely notice shorter startup and shutdown times. M2 users with a lot of mail will in addition benefit from the mail database reading optimizations that have been done to speed up startup.
Another big technological change is happening in graphics rendering. In Opera 10.10, VEGA (Opera's vector graphics library) is only used for rendering SVG. In Opera 10.5 VEGA is used for rendering all graphics in Opera, including content on webpages and the user interface. Currently VEGA is a pure software rendering engine, with the possibility to add hardware accelerated back-ends in future releases. But the software rendering is incredibly optimized, which means that Opera 10.5 has very fast painting performance even without using hardware acceleration.
People brave enough to test pre-alpha software can download the latest version of Opera over here.