For gaming purposes 4GB is a waste for 1366x768 resolution. However, the GT 750m is more powerful than the GT 740m so the laptop with the GT 750m should last you longer before you feel the need to upgrade. If the price difference is not very much then I would just go with the GT 750m laptop.
While I find that 1366x768 resolution is adequate enough for playing games, I find that resolution to be a bit too low to do other things. I have a Lenovo IdeaPad Y470 with a 1366x768 resolution screen which is the basis for my opinion.
I have been looking around for a 15.6" laptop with 1080p screen for a bit of time, but I stopped looking when my uncle decided to give me his 15.6" Dell Latitude 3450 with an i5-4200U, 1080p screen and Radeon HD 8850. I more or less fixed it for him, but he decided to eventually buy another laptop and so he gave me his Dell.
The Radeon HD 8850's performance is basically between the GT 750m and GT 755m. I find that it gives pretty good performance @ 1080p, but the only game I have been playing on it is Star Trek Online (STO). If the Radeon HD 8850 can handle 1080p pretty well, then the GT 750m should handle most games @ 1366x768 without much issue unless the game is extremely graphics intensive. STO is not the most graphically demanding game, but I have read it is one of best looking MMO games... people's opinion do vary though. Personally, as long as the game is fun to play, then I do not mind if the graphics are only considered "OK".