Back in the Apache/6700 days, there was a storage advantage to stuffing as much into the ROM as possible. Not anymore.
AFAIK, there has never been any speed advantage of OEM's over CAB's. It's just the convenience of not having to install those programs after a hard reset. Personally, I prefer to use sashimi or just manually install the cabs. Heck, in the old days we used to install programs one at a time, reseting in between to make sure each install worked right. As for the inadvertent hard reset, I keep 3 recent backup on my sd card. If I had to hard reset, I can be back up to speed in less than 10 minutes.