Memory consumption is way lower, think 30-40% lower. Fetch speed of queries without dependency injection in v2.5 is much much faster than 1.0.2005.1, I think 40-50% faster or thereabout. You also have much more tweakability: you can exclude fields now if you don't need them, which can enhance performance in hotspots if you fetch entities but don't need big blob fields at that point for example.
v1.0.2005.1 was slower because of the inheritance code implementation. Inheritance implementations slow down the queries a lot, relatively speaking. For example 1.0.2004.2 is much faster. In v2.0 we eliminated a lot of bottlenecks in the code, and in v2.5 we optimized even more elements.
There's no way we can optimize it even further without generating IL at runtime.