Well here's the data, see what makes sense for you @ your 2560x1080 resolution
With your resolution, the reference 1080 Ti is about 7-9% faster then the 2070.
https://www.techpowerup.com/reviews/MSI/GeForce_RTX_2070_Gaming_Z/33.html
I'll pick MSI Gaming X as TPU has testes both for the comparison
In UK .... 1080 Ti is £966.40 / 2070 is £519.98 ... I don't like new cards unless from someone you know well.
The MSI Gaming 2070 OC test realized a 12.62% gain
The MSI Gaming1080 Ti OC test realized a 14.66% gain
Overall that stretched the performance edge from 7 - 9 % to 9 - 11%
The MSI Gaming 2070 sound levels are 0 at idle and 30 dbA at load
The MSI Gaming 1080 Ti sound levels are 0 at idle and 35 dba at load (41% louder)
The MSI Gaming 2070 temps @ Load +OC are 70C
The MSI Gaming 1080 Ti temps @ Load +OC are 72C
The MSI Gaming 2070 Power consumption @ peak gaming is 233 watts
The MSI Gaming 1080 Ti Power consumption @ peak gaming is 303 watts ... @ 30 hours per week that's $28 (21 GBP) a year based upon UK 2018 average pricing
With a 75 Hz Freesync monitor however, more than likely, your monitor is not one of the few that support G-Sync so no luck w/ either likely. You also can't use Motion Blur (ULMB) or Ray Tracing with either card. If you had support, Ray Tracing would come into play on any game where you could get say 100+ fps. With RT eating a third of that, would bring you down to say 66 fps .... if you could hit 112, then RT would bring you down to about the limit of your monitor.
I don't see RT as an attempt to make older cards obsolete .... its just an added "free feature" same as 3D Surround, PhysX, ULMB. Here's an analogy, I walk into a dealership to buy a new SUV, they have two models on the floor.... my wife likies the blue one, I like the the white one but really don't care about the color.
The salesman explains that they are both the same price, same gas mileage, same acceleration. The white one has air conditioning, (analogous to PhysX in this example) blue one doesn't. Wife pipes in, "well it's not like every day you are going to need AC", I'm thinking "well it's there if I want it and it's not costing me anything". The salesman adds, the white one also has 4 WD (RT in my example), wife pipes in, "well it's not like every day you are going to need4WD all the time and it costs gas mileage", I'm thinking "well it's there if I want it, I'm not required to use it so doesn't have to cost me on mileage, it does improve riding on muddy jobsites and snow, and it's not costing me anything". Salesman adds "the white one has a performance package (ULMB) .... and it does have Eco and performance modes, wider tires, along with better headlights and a GPS system.". I'm not listening to my wife anymore
So, no I don't think these new features make older cards or vehicles "obsolete" but I do think that new features do allow for an improved experience. And these experiences are in no way diminished just because I may not to get a chance to use them every day. On that 95 degree day that I am stuck in traffic... I am going to tun on the AC and if the game supports PhysX, I am going to use it. If I see 75-80 fps, I am going to turn off G-Sync and use ULMB.... If I am seeing 160 fps, I am going to use RT.
If keeping your Freesync monitor for the forseeable future, Id get the 1080 Ti .... if the monitor is the next upgrade, it's a tossup. Another option would be the 2070 Ti.... if ya willing to wait till late summer / early fall and perhaps gran a monitor at same time.