This would not be too exciting Neither guy is tailor made for the other. Starling would try to make Pernell lead. But, Whitaker's "D" was so good, I don't think Starling would be able to land many counters. Starling would be physically stronger, with slightly better punching power. The judges would really have to pay attention. I think it could very well end up in a Draw.
Marlon, on point, could take this by decision. He had the skills to beat Pernell, but often, at times, his head wasn't in it.
Defence vs Defence. Two guys with exceptional feet work. Marlon with master tactician - Futch in his corner and a more aggressive offensive could nick it by a razors edge.
Two defensive fighters without much power or tenacity would make for a rather dull affair. Both were outstanding at what they did however. But the quicker and more talented Whitaker would have my vote to take a decision.
Some fights are competitive on paper, some are not. For example Liston always beats Patterson and Louis always beats Walcott. I favour Pea because I believe he always beats Starling.