Exactly how slow is asymmetric encryption? I'm currently doing a project on RSA, and have just come across this website.

https://www.namecheap.com/support/knowledgebase/article.aspx/798/67/what-is-an-rsa-key-used-for

On here, it says that 


  Since encrypted data transmission takes too much time in case of asymmetric encryption, this kind of encryption is used for a secure symmetric key exchange that is used for actual transmitted data encryption and decryption.


Now I was not aware that this was the case, so my question is, does this mean that asymmetric encryption is relatively slow compared to symmetric encryption, or is it impractically slow to be implemented in things like SSL?

Also, out of curiosity, exactly how much slower is it in terms of a time value?

Update:

Another question, why do the primes have to be far apart? I guess since the numbers used are so big they are far apart anyway, but is this a prerequisite for RSA, or just a fact that holds due to the size of the numbers?

Thanks
Yes, asymmetric encryption is slow compared to symmetric encryption. 

With symmetric ciphers, encryption and decryption speed can be several gigabytes per seconds on a common PC core; see these benchmarks.

With RSA encryption, on comparable hardware, we are talking tens of thousands encryptions per second, and only few hundreds of decryption per seconds, for common key sizes, and small messages (like 1 bit to 250 bytes, way enough for a session keys and authenticators); see these benchmarks.

Pure asymmetric encryption would often be like 3 to 5 decimal orders of magnitude slower than symmetric encryption is. That's the main reason why in practice, when enciphering messages that could be over what fits the capacity of a single asymmetric encryption, we use hybrid encryption.