The issue is probably your IGP. While the latest development revision should be less demanding on the CPU than 3.5, the latest development revisions require more from the GPU if I recall correctly. On lower spec'ed GPUs you'd notice a hit, in some cases even at 1x IR. Hopefully someone can verify this, as I haven't kept up with all of the GPU changes Dolphin has made recently.
Anyway, unless the latest development revisions get a sudden speedup, I think your problem is mostly hardware related, as the N2840 and its IGP are both on the weaker end of Dolphin's hardware spectrum.
Anyway, unless the latest development revisions get a sudden speedup, I think your problem is mostly hardware related, as the N2840 and its IGP are both on the weaker end of Dolphin's hardware spectrum.