Maximiliano Firtman (@firt) published a very comprehensive piece touching on performance, RWD, RESS, mobile web and more on SmashingMag recently rather provocatively entitled "You May Be Losing Users If Responsive Web Design Is Your Only Mobile Strategy". The whole responsive debate is something of an evergreen in web dev circles: where once the argument centred around UX and whether it was a good idea to serve the same content but reflow/hide some of it depending on screen size, now performance has become more of a leitmotif in commentary.
In reality, there may be a false dichotomy between RWD v non-responsive at play in some of the debate. Web development is a broad church and there are many options to choose from. Some things will always remain true when considering options for your web strategy.
Whether or not you use responsive or dedicated mobile strategy really depends on your business needs. If you need your mobile site to be different - in order to maximize quality of experience, UX, conversions - then make it different.
RWD can be optimized by using RESS or other techniques.
There is no reason that highly optimized content can't be served on the same URL based on an understanding of the device (non responsive) - google.com is an example of this.
Connectivity speeds can never be guaranteed