GSync vs FreeSync first... GSync is an NVidia technology solution while FreeSync is an AMD software solution. Both try to address the same fundamental problem - that graphics processors and monitors are basically asynchronous devices that, for best performance, need to be synchronised.
The symptoms of any synchronisation problems appear in two manifestations:
1) Monitor input frequency not same as GPU output frequency -> stuttering as monitor constantly tries to re-synchronise using sync pulse in signal
2) Monitor frame timing not synchronised with GPU frame timing -> tearing as monitor tries to display parts of two adjacent frames
The AMD approach (FreeSync) - which is elegantly simple - basically slows down the GPU's framerate to match the maximum framerate the monitor can handle. This is largely a software implementation and requires no proprietary hardware in the monitor to run. BUT it does result in unused GPU capacity. Final framerate will be fixed at compromise rate.
The NVidia approach (GSync) is a bit more complex as it is an "adaptive" (i.e. variable based on demands) synchronisation whereby the GPU needs to control the monitor (hence the proprietary technology aspect - for the GSync circuitry required in the monitor). In use, GSync relies on the GPU to "predict" the framerate demands of the application and to dynamically adjust the framerate and synchronisation of the monitor (up to its maximum capabilities).
This approach, while more complex, does tend to maximise the GPU utilisation in a synchronised system.
So, yes - the concepts involved in the symptoms displayed by monitors in situations of synchronisation error are common, these two approaches adopt two different philosophies to resolution. AMD's FreeSync approach is applicable across a wider range of monitors due its software-based approach, while the NVidia approach demands additional circuitry to be integrated into the base monitor - adding cost.
Both approaches have a dependency on which GPU you are using - FreeSync requires an AMD GPU while GSync require an NVidia GPU. So, if you already have a GPU that you are happy with, your FreeSync vs GSync decision has already been made...
If not... Think carefully and take into consideration all the implications of being tied to a bundled "approach PLUS graphics technology".
Next, as far as your conundrum is concerned - if you already looking at a gaming monitor of around 27" and 2560x1440p running at a real 144Hz it's more than likely going to have a response time of around 1ms and should, as a result of refresh and response rates, be reasonably immune to tearing and stuttering. Adding GSync to a monitor at 1440p which is already that fast, smacks of overkill. If you were looking at a 4K monitor, I'd be more inclined to agree to GSync as a 4K monitor has >8 million pixels per frame and that generates a whole lot of work for any poor GPU.
I guess the final decision will be down to a compromise between screen size, resolution, refresh rates, response times, and COST - and any compromise is basically a subjective decision - meaning you get to make it on your own...
I hope that helps
Dave