Hm, that does seem really strange. I had a Orinoco Gold Card for my Lombard, it worked well unless you used it for too long and it got hot. Then you'd have to wait for it to cool off.
Anyway, the only thing I can think of trying besides upgrading the firmware to Gold would be to try using Airport Drivers instead of the Orinoco Drivers. I'm not a hundred percent sure but I seemed to have gotten better range with the Airport Drivers. (I seem to recall a stability issue with the Orinoco Control Panel in either Mac OS 8 or 9... I can't remember, only that I liked the Airport Drivers better.)
Edit: Oh, I just noticed that you've got a PB5300 and 1400, you can use the Orinoco Drivers on one of them and see if it's the card, or if the drivers are not stable on Mac OS 9.
Anyway, the only thing I can think of trying besides upgrading the firmware to Gold would be to try using Airport Drivers instead of the Orinoco Drivers. I'm not a hundred percent sure but I seemed to have gotten better range with the Airport Drivers. (I seem to recall a stability issue with the Orinoco Control Panel in either Mac OS 8 or 9... I can't remember, only that I liked the Airport Drivers better.)
Edit: Oh, I just noticed that you've got a PB5300 and 1400, you can use the Orinoco Drivers on one of them and see if it's the card, or if the drivers are not stable on Mac OS 9.