We consider in this paper the problem of opportunistic scheduling of users employing orthogonal frequency division multiplexing (OFDM) with adaptive modulation and coding under the constraint that all sub-carriers are assigned to a single user during one time slot. We first present an optimal scheme which schedules the user with the best instantaneous channel conditions in order to maximize the system sum-capacity. The optimality of this scheme comes at the expense of a full feedback load and high number of channel estimations. In an attempt at simplifying the complexity of the system, we then present and study the performance of two switched-based scheduling schemes. Extensive and detailed numerical results are performed to illustrate the capacity-feedback tradeoff of the three schemes under consideration. These results show the switched-based scheduling schemes reduce considerably the number of channel estimations and the feedback load with a negligible loss in sum-capacity.