The B29 is the 3rd most difficult bomber to intercept. The first being the Ar234 and the second being the Mossi B Mk 16. But the thing about the B29 is that it has the best defensive guns in AH, AND it can mover at 360 TAS+ once the ords are gone at 28k and higher altitudes.
So, case in point if you're going to head to the industrial complex in bombers other than the Ar234, Mossi B Mk 16, or B29, you had better be taking along some decent escort fighters. The P47M/N models are second to none for that duty thanks to high alt performance, guns, and range. The P51B/D are also a good contenders.