Specifity in PCR? OK, so apparently my question has to be a certain length, eh, have a nice day! :)?

For PCR, the most important thing is to get a primer designed which has the exact logy with the gene /target sequence you are looking for. But at the same time, you need to take care of the fact that it needs to be unique, which means it should bind to only your sequence of interest as there may be a number of genes with identical or nearly identical sequences. Another parameter is your selection of the melting temperature. In general high Tm is desirable coz it neutralizes the occurrence of non specific binding. As in PCR you have a forward & a reverse primer, that means you are going to amplify a given stretch of DNA, that means you must have a fixed length for your amplicon product, & this would be constant & absolutely specific, though you may also get product fragments of smaller lengths, as the efficiency of PCR is never exactly 100%, but you should optimize it to be closer to 100%.