I don't know about table swapping, but if your workload involves a lot of updates and inserts, then the benefits of more memory are going to be limited by the write performance to disk. Or maybe not, if the default mySQL settings favor speed over durability.

i've done some more benchmarking and i wanted to post an update. for the applications i'm running, i've been seeing 4X+ performance gain moving from EC2 (small instance) to Linode. i'm not specifying which linode size because they're actually very comparable. you just need to get more memory or storage depending on your application's needs.

i also managed to benchmark Rackspace. i tried a few instances and found about a 2X+ gain with Linode across all the sizes. pretty amazing. another thing worth noting is that the first 4 times i launched an instance i got locked out due to some network issues. i spent maybe 45 minutes with online support and, although they were nice, they couldn't help me until eventually it "magically" fixed itself.

Rackspace is 2X EC2. Linode is 2X Rackspace. and the price is hard to beat when you consider the included bandwidth.