Sure you're not asking about the Z35? Acer Z35 is lower res (2560x1080), higher refresh capability (144Hz overclockable to ~200 reportedly). It's a VA vs. IPS type panel.
The Dell uses the same panel as the Acer XR341CK (freesync) and Predator X34 (Gsync) versions, but has neither. Among the Acers the Freesync tops at 75Hz while the Gsync version supposedly handles 100Hz.
Dell is reportedly calibrated out of the box, excellent color etc. per tftcentral and others, but much higher input lag.
Dell has a nifty effective built-in "KVM" capability with dual upstream USB connectivity. Not sure how quick it is to access thru the menu though.
The Acers all are VESA-mountable (the XR341CK had the mount plate in the box, I don't know about the Gsync X34, and did read in a review for the Z35 that you could get to a 100x100 pattern by removing plastic around the mount, although it wasn't entirely clear that was an 'approved' mod).
I have the Acer (XR341CK) and bought a 2-up/4-down USB 'switch' to behave as my "KVM", minus the V, between two computers. Haven't checked again recently but at the time I was looking at full KVMs none of them supported 3440x1440x60hz type resolutions, which of course requires displayport or extremely recent HDMI. I just kept a small separate panel for the 2nd computer's monitor (it's the controller for my 3d printer, not used as often as the gaming beast).
I'm aware as the Acer has an IPS panel I'm supposed to hate it for glow. But I'm too busy enjoying it to notice. Maybe because I was coming off a truly ancient 1600x1200 non-LED-backlit LCD that was always kind of soft with a fair amount of latency/trailing visible.
Mostly a FPS shooter player but not online - more story line. Or open/semiopen 3rd person games (Witcher 3 is current addiction, I'm letting all my GalPowers status totally expire in E:D lately....)
The Dell was on sale again at Newegg recently for $700ish. I have no idea how prices run for those outside the states though.
EDIT - one other difference I forgot that may not matter much to you. The Z35 has an external power brick (my XR341CK does too, presumably ditto on the Predator X34). The Dell doesn't - all power conversion is internal. Certainly a nicer arrangement, if that is a discriminator for you.
Edited by rtrski - 1/25/16 at 1:06pm