Does anyone have numbers on memory bandwidth and latency?

The x1 cost per GB is about 2/3 that of r3 instances, but you get 4x as many memory channels if spec the same amount of memory via r3 instances so the cost per memory channel is more than twice as high for x1 as r3. DRAM is valuable precisely because of its speed, but the speed itself is not cost-effective with the x1. As such, the x1 is really for the applications that can't scale with distributed memory. (Nothing new here, but this point is often overlooked.)

Similarly, you get a lot more SSDs with several r3 instances, so the aggregate disk bandwidth is also more cost-effective with r3.