There is definitely a different target customer and that matters. Rackspace customers are more likely to be classically architected n-tier web sites/apps and AWS customers are more likely to be fully "cloud architected".
The result of this difference is that a Rackspace cloud physical host is not going to be as heavily taxed resource-wise (at least on average). Add to that the cpu burst by default versus cpu cap by default and cpu is definitely the one area where differences will be widest.
One thing I will say though, and many may disagree with this, but I have yet to see a benchmarking study that I'd trust. Real world operating performance of a server is just a very complex thing and any attempt to distill it down to single parameter comparison is going to compromise some element of that complexity. I can show you comparison studies that show any of the cloud providers to be better than the others, including AWS, Rackspace, Linode, Joyent, etc. So take these things with a grain of salt.
> ny attempt to distill it down to single parameter comparison is going to compromise some element of that complexity
This is extremely true not just of this but of comparison in general. Turning something complicated into a natural number below 100 and then using > and < is pretty limited.
The result of this difference is that a Rackspace cloud physical host is not going to be as heavily taxed resource-wise (at least on average). Add to that the cpu burst by default versus cpu cap by default and cpu is definitely the one area where differences will be widest.
One thing I will say though, and many may disagree with this, but I have yet to see a benchmarking study that I'd trust. Real world operating performance of a server is just a very complex thing and any attempt to distill it down to single parameter comparison is going to compromise some element of that complexity. I can show you comparison studies that show any of the cloud providers to be better than the others, including AWS, Rackspace, Linode, Joyent, etc. So take these things with a grain of salt.