I own a Lenovo laptop with an I5-5200U, Intel HD 5500 (Iris Pro, Broadwell-U GT2) and an R9 m375 4GB (AMD Tropo) and I play GTA V with these settings:
4 units on distance scaling and 6 units on population density.
Texture and Shader Quality: Very High (which is highest)
Shadow: High (second highest)
Reflection: Ultra (highest again)
Water, Grass, Post FX: Normal (can be set to ultra)
Shadow Quality: Sharp (Highest is NVIDIA PCSS)
AFx16 and no advanced graphics.
No Ambient Occlusion, No AA except FXAA, No Tesselation.
It runs at around 35 most of the time but there are rare dips in areas and moments like an explosion when it dips to 21. It was very playable.
An R9 m375x (AMD Tropo XT2) is a weaker GPU than a GT 940M.
I'm guessing with a GT 940M, you'd be able to turn these settings higher:
Resolution: 1600*900 or maybe lower
Shadow: Very High (highest than can be set)
Water, Grass, Post FX: Very high
Shadow Quality: Softest (looks better and doesn't affect performance that much)
High AO, for AA I'd say FXAA, Tesselation high.
A GTX 970 runs GTA V with highest settings (no including MSAA, TXAA and such stuff) at 1920*1080 well over 60 fps all the time.
So a GTX 950 could do around 30 fps at 1080p highest (no MSAA, TXAA) GTX 950 is slightly more than powerful than GTX 660Ti and noticeably more powerful than PS4 GPU (HD 7850-7870).
So a GT 940m should do it around 20 fps right? Turn the resolution down to 1600*900p or 1366*768 and I can guarantee that you'll be golden.
Just keep an eye for the VRAM. GTA V at these settings consumes more VRAM than 2GB.
What you need to turn down is AA (go with FXAA and no MSAA or TXAA). Don't worry, it's a Maxwell GPU after all!