For a gaming laptop, I prefer a 17" screen, but that’s probably going to put it out of budget for the other specs you want, and probably will make less difference. (Also, it makes for a bulky beast of a laptop, I’ll admit.)
I’m not a Dell fan, and you don’t want to compromise on video for a game box. I’d stay away from this option.
The Sager is actually a branded Clevo P650, and I’ve generally had good luck with my Clevo gaming laptop. Also, I see good reviews on its cooling capability, which is a big deal with gaming machines. (Mine cools fine, but is very noisy under load; the reviews suggest the 650 is much quieter.) It only offers the 3GB version of the 970M, while the VenomX P35WV4 comes with the 6GB version, but I don’t know that it actually makes that much difference. For an otherwise equivalent build, the Sager looks like it would be the cheaper option. Of the two, I’d lean toward the Sager.
The recommendation you got on SSD is a good one. It makes a big difference to have your games loaded on an SSD drive–I recently upgraded, and the change to load times was amazing. The choices here get a bit complicated, and may depend on what else you do with the laptop.
Expand the mSATA drive, where your OS lives, to also hold your games. Keep the regular HDD for mass storage (movies, music, documents, whatever doesn’t need fast access). This would increase the price of the Sager build to $1,574. Downside: The mSATA is SATA2, so the connection to this drive is only half as fast as to your SATA3 bay, where the big drive is connected. Sharing space among OS, apps, and games may also require you to do more active space management (i.e., you may not be able to keep as many games installed at once).
Leave the mSATA alone and swap the HDD for an SSD. This will put your games and stuff on a SATA3 SSD, which will get your best performance, but it will cost you in total storage space. Swapping the HDD to a 500GB SDD will make the price $1,539. A 1TB SSD would raise it to $1,749–outside your stated budget.
Downside: You lose a lot of storage space.
Leave the build as-is. Your cheapest option at $1,399, keeps the storage, and you can probably put at least some of your games on the OS-drive. Downside: Less performance boost than having a separate SSD, and you may have to uninstall stuff more often to make room. (A lot of games are space-hungry, but Minecraft and Metal Gear should fit easily.)
I basically went with option 2 when I upgraded recently, and I’m pretty happy with it. I have a 500GB SSD, and I mostly keep movies, music, and so forth on an external drive.
Random tip: Learn the hotkey to disable the touchpad. It’s big and placed where you’ll accidentally brush it a lot, which can be frustrating whether you’re gaming or typing. Turning it off when you don’t want it will save you a lot of annoyance. (On mine, Fn+F1 toggles it.)
ETA: On the Sager builds I priced, I bumped the RAM up to 16G, partly to match the VenomX and partly because I really like lots of RAM.