I see a few difference.
1. Mayweather is a better offensive fighter than Pernell.
2. Mayweather isn't as awkward of a fighter so it will seem easier for Oscar Dela Hoya, but I don't think he will be able to catch PBF.
3. Like you said Oscar is alot older and MAyweather is faster than Pernell to begin with so the speed differential in this fight is far greater.