Can’t help you with OpenCL, this is a CUDA forum. CUDA ships with an example program called deviceQuery. Run it, and look for the following line in the output:
If it says 2 copy engines, the GPU supports full-duplex DMA transfers across PCIe. The above output is from a Quadro K2200 (basically a glorified GTX 750 Ti), and it has only one copy engine available. Based on that it would be extremely unlikely that the GTX 750 supports more than 1 copy engine.