Earlier quoted context omitted.
If it's low RAM and single threaded then I would expect every tier to perform identically. (Also I was just looking at the pricing, you don't get any extra CPU cores until the $84 tier!)
Thanks for pointing that out. I had thought maybe as the tiers went up you'd get faster CPUs, but upon reflection the pricing schedule seems to confirm your point. I guess they are completely virtualized because there is not mention of CPU type on the pricing page.
Which makes sense with the policies many providers have against actually utilizing all the CPU you paid for.