If you get a "Error CL_MEM_OBJECT_ALLOCATION_FAILURE" try increase virtual memory in windows.
Go with number of GPU's * 8gb + 8 , for example 6gpu * 8gb + 8 = 56gb virtual memory.
Regarding the tweaking profiles, you must find the right profile for your weaker gpu's not every card can handle the same profile number.
You can do that in gpu_conf, for example :
"gpu_conf" :
[
{ "id" : 0, "intensity" : 124, "worksize" : 16, "tweak_profile" : 10, "threads" : 2},
{ "id" : 1, "intensity" : 124, "worksize" : 16, "tweak_profile" : 10, "threads" : 2},
{ "id" : 2, "intensity" : 124, "worksize" : 16, "tweak_profile" : 6, "threads" : 2}
]