The engine inlet is about Mach 5 if I calculated things correctly and use the assumption that the shock cones will be able to move all the way back out when the shock has been captured on the mouth of the engine inlet.

This can also be somewhat confirmed by the pilot reports that noted a reduction in fuel burn when they accelerated past Mach 3.2 to evade missiles.

Now as far as the airframe, that depends on if you want the bow shock to remain clear of the entire airframe, or if you allow it to touch the outer edge of the mouth of the engine inlet. The 3-views I found seem to indicate somewhere just over Mach 4 with 5 a possibility if you let the bow shock reach the edge of the engine inlet.

I haven't had to make this calculation in about 8 years and I don't have a protractor handy, so I could be off a bit.