gtx 860m 4g ddr3 vs gtx 960m 2g ddr5

Solution
Excluding RAM, the performance of the GTX 960m will be slightly better than the GTX 860m because of slightly higher clockspeeds.

However, DDR3 RAM is slower than DDR5 RAM so that is going to bring down the performance of the GTX 860m. That is based on a comparison between the desktop Radeon HD 6670 with DDR3 and Radeon HD 6670 with DDR5 from several years ago. The Radeon HD 6670 was a mainstream GPU back then and the comparison showed the DDR3 version had about 25% less performance than the DDR5 version. The more powerful the graphics chip, the larger the difference in performance will be.

The amount of RAM is meaningless if the RAM itself is slowing down the graphics chip.
Excluding RAM, the performance of the GTX 960m will be slightly better than the GTX 860m because of slightly higher clockspeeds.

However, DDR3 RAM is slower than DDR5 RAM so that is going to bring down the performance of the GTX 860m. That is based on a comparison between the desktop Radeon HD 6670 with DDR3 and Radeon HD 6670 with DDR5 from several years ago. The Radeon HD 6670 was a mainstream GPU back then and the comparison showed the DDR3 version had about 25% less performance than the DDR5 version. The more powerful the graphics chip, the larger the difference in performance will be.

The amount of RAM is meaningless if the RAM itself is slowing down the graphics chip.
 
Solution