Michael Irvin was a 4.5 guy. His lack of speed didn't hurt the Cowboys. I think being open, whether it's 10 yards down the field or 40 yards, is more conducive to the running game working than the deep play. Cowboys have Beasley, Switzer and Williams to get first downs, not to mention if Gathers, Jarwin or Swaim develop into reliable targets.
But I'd love to have a 4.3 receiver on the team, always good to have every factor on the field, but I think with the prevalence of the West Coast offense most teams run, and especially the Cowboys with a run-first scheme, that speed at the receiver spot is a bit overrrated...