No it isn't, that's a completely meaningless answer. You might be able to afford £1000 a month, that doesn't mean that's the answer to how much you should spend on a PCP for a 1 Series, does it?
The real answer is whatever monthly payment results in the lowest possible TCO (Versus other ways of running the same or similar vehicle), plus a small amount added for the convenience of PCP, IMHO.
There is much mystery mis-truths spouted about PCP's, mostly by those who like PCP's and like to convince themselves PCP's are the best thing ever.
People like PCP's because the offset enormous balloon payment puts them into cars they couldnt afford any other way. A PCP will typically have the highest TCO of any method of purchase bar leasing. The dealer/manufacturer contributions are still available with HP, which almost always costs you less over your ownership duration. But of course the monthly payment is higher with HP...