That would depend on the type of CPU Linode is using. What the CPU's frequency is, the amount of cores, whether it has or does not have hyper-threading technology.

The hyper-threading technology is a pretty cheap way to add more virtual cores to your VPS's which is great. One thing is for sure and that is that Linode provides you 4 virtual cores and not 12 per VPS. But, that of course doesn't mean their CPU is better or worse. But, if you can run 6 cores at 3.8ghz, or 12 cores at 1.9ghz then I wouldn't worry too much about not having enough CPU power for your virtual private servers.

If any CPU-overcommitted VM system has guests which all want 100% of the CPU, they'll all suffer. No two ways about that. I don't know what hardware Linode put their 512MB instances on, and I don't know their overcommit ratio. 128 is more guests than I'd put on a 64GB host, though.

If your typical load is actually at 100% CPU for the majority of the time, I'll go out on a limb and suggest that VPS might not be the best bet anyway.