The two go hand in hand if applied correctly, which unfortunately the Blackbird wasn't, it's all about reaction time. If a radar first tracks a conventional plane at 300 miles out from a target moving at 600mph the defence will have half an hour. But for an SR71 the stealth measures may mean it won't get picked up until 200 miles from target, and moving at 2000mph gives the defence 6 minutes to react.
Ideally the 60s stealth plane won't go Mach 3 because of the stealth reducing-effects that creates; ionised radar-reflective exaust plume, vast heat signature. Something which cruises subsonically until detection values are reached and then guns-it to mach 2-2.5 over the last 150 miles or so (an arbitrary figure, I don't know how much 60s stealth would decrease detection ranges) would get the best of both worlds in the circumstances.