Right, Calahan's EPIRB was likely a 121.5MHZ EPIRB but while it was theorized that nobody was close enough to hear it, it was also theorized (by Calahan himself) that it malfunctioned. In other cases where a survivor went into the raft and the EPIRB did malfunction it's likely that we never got to hear their story because they eventually became shark poo....
Most people who rely 100% GPS and don't have a sextant aboard carry multiple GPSs for an offshore trip. I think the same logic should be applied to EPIRBS and multiples should be carried if you aren't packing all the other equipment required for a lengthy raft trip.
Another idea I had to effect a quicker rescue would be to invest in a handheld ham radio. They come in submersible versions for around $300 (the cost of a PLB) and non-waterproof ones for around $100.
The reason for handheld ham is that you can see aircraft overhead by their strobe lights and could call them on the international aircraft distress frequency and they could relay your mayday, verify your position etc. Or, as recently seen in the news they could fly down and spot you themselves.
The handheld HAM also doubles as a VHF helping you affect your rescue directly when you sight a ship and also allowing you to alert rescuers via contacting a plane.
For those concerned about not being HAM licensed, it is not a crime for a non-HAM to use a HAM radio and or frequency in an emergency. It would behoove you though to familiarize yourself with the radio beforehand as they are usually more complex and intimidating than a VHF.
For the technologically inclined I would thing the following would make a good minimum kit for getting found and rescued. Prices are retail and can be found cheaper:
PLB 406MHZ $300
Handheld waterproof VHF $100
Handheld waterproof GPS $100
Handheld non-waterproof HAM radio and waterproof radio bag $150
$650 and a few extra dollars for the fanny pack it would all easily fit in.
This allows you a primary method of alert (the sattelite PLB) with a backup (using the HAM to call airplanes). It allows you a primary method of helping your rescuers (using the VHF to direct the ship to your tiny raft and talk about the boarding plan) and a backup in the form of the HAM. The GPS helps augment the radios as you can tell the rescuers exactly where you are and your rate of drift. Anything you would add to this, like a full EPIRB or backup PLB or VHF would all be to the good.