I've never heard a correlation between beta levels and heartbeat, but I'm curious to know the answer to this. My clinic doesn't measure hCG levels after the first few confirmations of pregnancy, so I have no idea what mine were at 5 weeks 5 days, which is when I first saw the heartbeat... IF my levels had continued to double during the time between my last beta and first ultrasound, they certainly would've been over 10,000, but I also know the rate doesn't continue to rise at the same rate..
Regardless, I was told at 6 weeks there would be about a 50/50 chance of seeing the HB, so don't panic if you don't see one! Good luck.