When I applied for those loans, I usually got rejected. An hour later I'd get a call offering me it at 8.7%. Reading on forums such as money supermarket it's a common thing.
I'm a good earner with a great credit score.
5.9% pcp is still pretty good to be fair. My friend took out a pcp on the default 10% ouch!
I bought mine on PCP initially to get all the deposit contributions and to keep the initially monthly payments down whilst I got used to owning a car again (I'd been a company car driver for the previous 16 years). I put £10k deposit down (which was basically the maximum BMW would permit) and I bought the car outright from BMW FS 14 months later with the above personal loan. If you can get the PCP finance at 3.4% I'd take that in a heartbeat. I doubt you'll finance such a large purchase st a lower cost if you haven't got the cash in the bank.