847/5000
Hello, the post is old but I hope someone find this info useful, since these notebooks are currently getting very cheap.
I have the same notebook Lenovo G400 20235, [but it came with a core i3-3110m, integrated intel HD4000 and intel WiFi card], I have successfully tried an i7-3632QM and a i7-3520M, both work OK. I have also tested it with Hyperx Impact Black memories (Kingston) DDR3L 1600 16Gb kit (2x8Gb) working OK. A friend also had the same Lenovo G400 but his came with a Celeron installed, that notebook did not accept the i7, not even the i3 that I uninstalled, also did not accept the 16Gb of RAM (only accepted 8Gb, either a single module of 8Gb or two of 4Gb).
I hope this helps someone.