error is already on par with the best available composite methods 18 and is further slightly reduced adding CBS and CV contributions by inexpensive MP2-F12 computations. These trends confirm that two-point extrapolation at the MP2-F12 level is an effective route for estimating the CBS limit without introducing additional computational bottlenecks with respect to the underlying CCSD(T)-F12/j3Z reference. As a matter of fact, already for reactions involving two heavy atoms, junChS-F12 computations require no more than twice the time of the CCSD(T)-F12/jun-cc-pVTZ step and are one order of magnitude faster than their CBS+CV counterparts. It is also remarkable that all the energy barriers showing non negligible errors have quite large contributions from full triple and perturbative quadruple excitations (fT+pQ), which are not included in the junChS-F12 approach nor in its CBS+CV counterpart. Table collects also the differences between anharmonic and harmonic ZPE contributions to energy barriers (∆anh). While these terms (together with spin-orbit contributions) will be discussed in more detail in the following, we already point out that their contribution is sometimes comparable with that of (fT+pQ). Two larger compilations of energy barriers are available for prototypical reactions involving the transfer of hydrogen (HTBH38/08 ) and non-hydrogen atoms (NHTBH38/08 75 ), respectively. However, the values not already included in the DBH24 set have been obtained at a lower computational level (W1 ). In order to investigate the role of different effects on energy barriers we have computed Best values for all the reactions belonging to those two sets. It is noteworthy that rDSD energy barriers, although not directly used in the junChS model chemistries, show mean unsigned errors (MUEs) smaller than 8.0 kJ mol -1 , thus suggesting that the corresponding geometries should be sufficiently accurate for single-point energy evaluations at higher computational levels.