I'm still testing these Atom based configs and tried most of the old and modern o.s. combinations. I usually tested the low end version without HT with a clock of almost 1,9Ghz dual core SSSE3 SoC having the "famous" GMA36x0 (PowerVR SGX 545 based architecture integrated into it) I've tested so many times to have some opinions. Its x64 CPU was one of the last old Atoms based concept for late netbooks or industrial boards. From a CPU speed point of view we could compare these to some late Pentium4 with 10 watts of power and like 2-3 watts for its GPU.
The problems came with the iGPU situation compared to the older Atoms GPUs that at least had solid driver support and retrocompatibility. The GMA36x0 iGPU was instead based on the SGX545 mobile IC and probably more oriented to OpenGL ES low resolution mobile based config instead of any desktop-like gaming one not to mention once Win7 already released with WDDM modern driver requirements. On paper it had everything to be a Directx10.x / OpenGL 3.x notebook like GPU but maybe the idea of having a smartphone iGPU on a x86/x64 scenario needed (too) much more work into the drivers to get an acceptable compatibility not to mention speed. It's difficult to compare such different architecture; on Win7 32bit the latest driver solved many problems with a speed sometimes close to a (very) slow Radeon 9500 and not a great retrocompatibility and what felt like a very complex driver layers/heavy situation like when using an "API wrapper" to explain its speed. And the syntethic benchmark numbers were low and beside good Pixel Shaders results/speed, fill rate resulted very low, even lower in multitexturing.
Games like Doom3 or Far Cry ran at like 15-20fps at 800x600 more or less. 3DMark05 got a 700 points like result. Old games in Win7 already needed some retrocompatibility o.s. fix (like DirectDraw) to add to the already complex driver situation so it was not difficult that old games were slower than modern ones. For what I remember reading opinions around, this different architecture may have needed specific game level optimizations to get better results and the architecture design was scalable but the one integrated into the SoC wasn't even close the fastest possible option (maybe costs, SoC space, less unified shaders/clocks/power requirement).
XP had some beta drivers I think and not 3D support; Win7 x64 had early beta driver that didn't get far while the x86 one was supported until late 2013. So the only o.s. for this iGPU has been Win7 32bit. On linux the situation was really bad; few Ubuntu 12.04.1 LTS proprietary drivers existed for the 2D part not 3D. Nowdays a compatible basic 2D cpu based driver still exists without accelerations. At the end using these was like the "Rage Mobility on AGP" cards where low power video ICs were used on desktop PC to get low speed waiting for newer drivers. The power required by this iGPU at least measured with a meter explain most of the questions. This iGPU serie has been probably the lowest power video chip in a desktop config ever and not much could have been expected when compared to 10x more power demanding GPUs.