Thanks guys!
Well, no surprise here, my single core score under Benchmark 5 is.... (drum roll) : 239
:'(
EDIT : can expanding RAM help in my case or is it useless because it's all about the core processor ?
Well, that pretty much explains your problem. Do you have your OS on an SSD? That would probably help more than additional RAM. I believe you already have 8 GB of RAM, which is more than enough to run BIAB on Win 10 64-bit. But I think you would be better off getting another PC---either a refurbished one from TigerDirect (as Mario had suggested) or a refurbished Dell minitower. I bought my mother a refurbished Dell Optiplex 7100 or 7200 with an i3 two years ago for only $189 with free shipping and a 90-day warranty. That PC is about as fast as my Optiplex 780, but they have a lot of other PCs that are much faster than that, and I'm sure TigerDirect does, too. You should be able to find a decently-fast PC for $200-300 that will keep you going for 5-10 years, especially if you put a 500 GB Samsung SSD in it.