I want to respond to this thread because it came up while I was doing some searches on a related topic and it doesn't appear that anyone was satisfied with a particular answer. My credentials are CFI/CFII, Remote Pilot Certificate, airplane owner and operator, drone owner and operator and Juris Doctor Candidate (graduating this May). Note: I cannot provide legal advice, and this should not be construed as such.
TL;DR - The statute that you would be violating if you are operating a model aircraft for recreational purposes beyond 5 miles from the primary airport associated with Class B airspace yet within the Class B airspace itself without authorization to do so would indeed be 14 C.F.R. § 91.131 (or, as has been said, through § 101.43 utilizing § 91.131 as indicia of endangering the NAS).
The following is from the FAA's "Interpretation of the Special Rule for Model Aircraft" which is located here:
https://www.faa.gov/uas/media/model_aircraft_spec_rule.pdf
As discussed above, if a model aircraft is operated consistently with the terms of section 336(a) and (c), then it would not be subject to future FAA regulations regarding model aircraft. However, Congress also recognized the potential for such operations to endanger other aircraft and systems of the NAS. Therefore, it specifically stated that
“[n]othing in this section shall be construed to limit the authority of the Administrator to pursue enforcement action against persons operating model aircraft who endanger the safety of the national airspace system.” P.L. 112-95, section 336(b).
...
Reading the broad reference to the NAS, along with Congress’ clear interest in ensuring that model aircraft are safely operated, we conclude that Congress intended for the FAA to be able to rely on a range of our existing regulations to protect users of the airspace and people and property on the ground. Therefore,
regardless of whether a model aircraft satisfies the statutory definition and operational requirements described above, if the model aircraft is operated in such a manner that endangers the safety of the NAS, the FAA may take enforcement action consistent with Congress’ mandate.
IV.
Examples of Regulations That Apply to Model Aircraft
The FAA could apply several regulations in part 91 when determining whether to take enforcement action against a model aircraft operator for endangering the NAS.
The FAA's general operating and flight rules are housed in part 91 of the FAA's regulations. These rules are the baseline rules that apply to all aircraft operated in the United States with limited exceptions, and are the appropriate rules to apply when evaluating model aircraft operations.
...
Rules governing operations in designated airspace are found in §§ 91.126 through 91.135. In general, those rules establish requirements for operating in the various classes of airspace, and near airports in non-designated airspace to minimize risk of collision in higher traffic airspace.
Generally, if an operator is unable to comply with the regulatory requirements for operating in a particular class of airspace, the operator would need authorization from air traffic control to operate in that area. 
