For what it’s worth I picked up a PC with a mineable graphics card last weekend and set it going with the new experimental GPU miner overnight head to head with the CPU miner. Here are the results:
Windows 7 x64 latest build with SP/updates…
ATI/AMD Radeon R5 240/HD 8570, 266/19/2/0/0, 0.005 XPM/hr
Intel Core i7-4770 - 8 threads - Xolominer v1.1, 103/7/2/0/0, 0.003 XPM/hr
The GPU returns about double the CPU, but this is only part of the story; the power consumption of the PC was significantly greater with the GPU miner running, more than double, so if you pay for power the ROI may actually be less.
There is also a small bug: changing the THREADPRIO does not work; the actual thread priority remains “normal” even thought the miner reports using High or Low priority. With a thread priority of “normal” the PC becomes next to unusable, but manually changing the thread priority to “below normal” resolves this. Note that the CPU miner defaults to “below normal”.