Am just a beginer and realy catching up well. but i encounterd a problem with refference modeling. after loading a background pic. i observed moving vertses becoming very slow, i would realy appriciate more tutorials on refference modeling or anything to solve my problem.
Chances are your reference photographs are large, and your system has a relatively small amount of RAM. Blender has to allocate memory to display the photos, so if they are big, the amount of memory left over to handle verts is reduced.
Try reducing the size of the reference photos using the Gimp or IrfanView. In IrfanView use Image>Resize/Resample, in the Gimp use Image>Scale Image.