  The determination of theoretical error estimates and PDF/$\alpha_S$-fits
require fast evaluations of differential cross sections for varied QCD input
parameters. These include PDFs, the strong coupling constant $\alpha_S$ and the
renormalisation and factorisation scales. Beyond leading order QCD, a full
dedicated calculation for each set of parameters is often too time-consuming,
certainly when performing PDF-fits. We report on two methods to overcome this
issue for any QCD NLO calculation: The novel event-reweighting feature in
Sherpa and the automated generation of interpolation grids using the recently
introduced MCgrid interface. For MCgrid we present the newly added support for
fastNLO tables and highlight some future developments.
