The mapping spaces of the r-truncated versions of the E_n operads appear as the r-th stage of the Taylor tower for long embedding spaces. It has been shown that their rational homotopy groups can be expressed through graph homology in the limit r\to \infty. For finite r only a part of the graph homology appears in the homotopy groups of the Taylor tower at this stage, possibly along with some additional unstable homotopy groups. In this paper we study the convergence properties in some more detail. In particular, we provide bounds for the stage r at which the various graph homology classes start appearing, and we provide degree bounds for the unstable (i.e., vanishing as r\to \infty) terms in the homotopy groups of the tower.