I'm pretty certain that 27 x 1 1/4 paselas AREN'T rated for 50 PSI AT ALL.
A 50 PSI tire is typically the very heavy-duty type of tire that weighs at least 400 grams with 60 threads per inch and is so stiff that it would tend to keep the bike off the ground even without air in the tire! Panaracer pasela tires have very thin and lightweight casings, are very low-profile, and are very much like a racing (Conti 4000 or Michelin ProRace3) and imho are not designed AT ALL to work at less than about 90 psi, and more typically at 100-110 psi. Note that on the Panaracer website, the TG tires are designed as "Extreme Light" tires!
To handle 50 psi I think you need a high-profile tire! If you want to run a 50 PSI tire, then I suggest something like the $7.99 kenda tires that actually say 50 psi or 60 psi on the sidewalls
As for hook-bead vs. kevlar tires - - - I have some Rigida 1319 rims which are hooked, but my kevlar tires (Clement Ventoux) still blew off the rims (both tires, same ride, start and end of the ride) after they were pumped up with an on-topic and silca pump ... perhaps it's because the tires were actually thai and the silca pump sabotaged them?
- Don Gillies
San Diego, CA