Ultrawide without, or smaller monitor with G-Sync

[big_treacle]

I'm looking at a new PC & currently the Battlebox Titan looks like a pretty good deal.

I need a monitor to go with it but I'm torn between an ultrawide with no G-sync or something slightly smaller with G-sync. I have a budget of about £700 so I'm looking at something like
this G-sync 2560x1440
vs
this 3440x1440 without G-sync

I'll be playing stuff like Battlefield, driving sims, Civ & using it for development work. Ideally I'd want to be cranking the games up to full whack.
i guess the question is, do I need G-Sync with this sort of system or will it be fine without? What would give me the best experience?
Thanks

 

[big_treacle]

Thanks for the help.

I went for the S2716DG in the end