I'd like to see some facts to back that up: I suspect it is bunk, another problem somewhere that has been mistakenly attributed to the certificate type (perhaps they altered other SSL options on their web server at the same time as changing the cert, or the non-EV cert uses smaller keys so takes less CPU time to process).

The EV certs contain extra information so are likely to be a little larger, but we are talking at most a couple of hundred bytes here so the extra download time getting the cert and CPU time verifying things are not going to be significant.

People do tend to have larger key sizes on EV certs (2048 or 4096 bit rather than 1024 or 2048 (though 1024 bit keys are increasingly rare even for "standard" certificates)) which might impose a measurable latency difference on a mobile (or other low-power) device due to the math involved in verifying the site against the certificate, but nothing like the order of magnitude that link mentions.

Because the browser is going to check if the certificate is revoked as part of the ssl handshake. We have gotten sites being not available because the service that the browsers use to do this validation were not responding fast. The handshake took up to a minute.