Asynchify or Synchify?

Asynchronous methods are a powerful productivity tool, enabling you to write scalable and responsive libraries and applications. It should be considered that asynchronicity is not a performance optimization for an individual operation. Taking a synchronous operation and making it asynchronous will invariably degrade the performance of that one operation, as it still needs to accomplish everything that the synchronous operation did, but now with additional constraints and considerations.

How the Overall System Performs when Everything is Written Asynchronously?

The performance of your application will be increased by using asynchronicity in the aggregate because you can overlap I/O and achieve better system utilization by consuming valuable resources only when they are actually needed for execution.

Async CTP Optimization

The asynchronous method implementation provided by the .NET Framework is well-optimized, and often ends up providing as good or better performance than well-written asynchronous implementations using existing patterns and volumes more code. Any time you are planning to develop asynchronous code in the .NET Framework from now on, asynchronous methods should be your tool of choice. Still, it’s good for you as a developer to be aware of everything the Framework is doing on your behalf in these asynchronous methods, so you can ensure the end result is as good as it can possibly be.

Async CTP
When your user interface is unresponsive or your server doesn’t scale, chances are you need your code to be more asynchronous. With today’s .NET Framework and language features, though, that is easier said than done.
The Microsoft Visual Studio Async CTP proposes a new language feature in C# 5, and a new framework pattern to go with it, that will make asynchronous programming similar to – and about as straightforward as –synchronous programming.
The goal is to bring the asynchronous development experience as close to the synchronous paradigm as possible, without letting go of the ability to handle the asynchrony-specific situations. Asynchrony should be explicit and non-transparent, but in a very lightweight and non-disruptive manner. Composability, abstraction and control structures should all work as simply and intuitively as with synchronous code.