You mention that you only had to use airodump-ng to listen to the AP and then aircrack-ng to crack the key. The reason this worked is that there were currently other client(s) connected to the AP generating the actual traffic for you to capture. As aireplay-ng is only used to generate traffic and speed up the capturing process of the needed ivs this part can be left out, but the process will then be much more time consuming as you have to rely on other clients to generate the needed packets.
The packetforge is used to create an valid ARP-packet to be used with aireplay-ng. This packet can then be broadcasted over and over to the AP, which will respond with the ivs that you will need to actually crack the WEP key. There are also several other methods available with aireplay-ng, of which the ARP-replay is probably the most used and in most instances also fastest one, that do not at all require the use of packetforge-ng.
You also ask whether the KoreK attack is more silent or efficient than the never PTW method. As both of these methods only come into play at the very last stage of the process, the actual calculation of the WEP key, nothing will be broadcasted using either of them and they are therefore both completely “silent”. Apart from this the KoreK method is actually slower than the new PTW method and will usually require both more time and individual captured packets to find the WEP key. On the other hand the PTW method does have some limitations and the KoreK method is therefore at times is the only option, which is why it still is included with aircrack-ng.
As for the caption of the thread, Why do I need packetforge-ng for KoreK?, the short answer is that you do not.