  We compare analytical computations with numerical simulations for dark-matter
clustering, in general relativity and in the normal branch of DGP gravity
(nDGP). Our analytical frameword is the Effective Field Theory of Large-Scale
Structure (EFTofLSS), which we use to compute the one-loop dark-matter power
spectrum, including the resummation of infrared bulk displacement effects. We
compare this to a set of 20 COLA simulations at redshifts $z = 0$, $z=0.5$, and
$z =1$, and fit the free parameter of the EFTofLSS, called the speed of sound,
in both $\Lambda$CDM and nDGP at each redshift. At one-loop at $z = 0$, the
reach of the EFTofLSS is $k_{\rm reach}\approx 0.14 \, h { \rm Mpc^{-1}}$ for
both $\Lambda$CDM and nDGP. Along the way, we compare two different infrared
resummation schemes and two different treatments of the time dependence of the
perturbative expansion, concluding that they agree to approximately $1\%$ over
the scales of interest. Finally, we use the ratio of the COLA power spectra to
make a precision measurement of the difference between the speeds of sound in
$\Lambda$CDM and nDGP, and verify that this is proportional to the modification
of the linear coupling constant of the Poisson equation.
