I'm just succesfully flash stock rom to my brother Lenove A850+.
I'm going to share the steps i found works.
It's for my note too.
pic from GSMArena
Flashing stock rom Lenovo A850+
Just follow the steps below.
1. Download the ROM File
http://firmwarefile.com/lenovo-a850-plus
http://firmwarefile.com/lenovo-a850-plus
2. Install any related drivers on your PC.
Android USB Drivers. (skip if already installed) =>
MTK USB Driver (In order to flash using flash tools)
https://androidmtk.com/download-mtk-driver-auto-installer
3. Get SP Flash Tools
https://androidmtk.com/smart-phone-flash-tool
https://androidmtk.com/smart-phone-flash-tool
Flash Instructions
I'm just made untill this step.
Heard the rumor u can use LuckyPatcher for the PlayStore.
Install PlayStore using LuckyPatcher (not sure if its works)
Thanks and good luck flashing.