Just keep in mind your use case. If it is just the R7000 covering a multistory dwelling, do NOT get antennas bigger than the 5dBi omnis that came on it. The higher the gain, the more compact the radiation pattern and gain is on the antenna. So things above and below it are going to receive worse signal, while things on the same level will get better signal.
In my experience with significant testing, on one router moving from 3dBi to 5dBi (Archer C8) and on another router (WDR3600) moving from 5dBi to 7dBi antennas resulted in roughly an average gain of 20% more throughput on 5GHz and a little less on 2.4GHz at medium to extreme range indoors. The Archer C8 also saw 5GHz gains at short range in 11ac operation (only about 10% though), but the WDR3600 saw no short range gains 2.4/5GHz and the Archer C8 doesn't show any improvements in 5GHz 11n operation at short range.
Just briefly trialing the 7dBi on the Archer C8 (so a 4dBi increase over the stock antennas), I only saw a slight gain over the 5dBi. It was roughly a 30% increase over the 3dBi (so, call it 10% above the 5dBi) and there was no extra gain at short range on 5GHz 11ac operation at all over the 5dBi (still the same rough 10% gain over the 3dBi).
I didn't notice any real increase in range inside my house on 2.4GHz, though on the Archer C8, with 5GHz I did get usable signal at one location where I couldn't do anything previously (I could connected, but the connection was intermitent at best. With the 5dBi it is now low signal strength, but on my laptop with 11ac I can get 3.8MB/sec down and 1.2MB/sec up. With the 7dBi I can get 4.2MB/sec down and 2.3MB/sec up).
Anyway, the gains are certainly enough that in my mind it makes sense to bump antenna size a bit if you have the coverage required for it. One thing I did run in to with the 7dBi antennas on my WDR3600, along with shifting the router over a bit so that my chimney was not in the way, I then had to bump the radio power on 2.4GHz to minimum, otherwise my devices would not roam to my basement router when on the other side of the house right above the router (even though the signal strength was stronger on the basement router, the first floor AP was strong enough they didn't want to switch). This wasn't as much of an issue with the 5dBi antennas that came with the WDR3600. That said, the difference between minimum and maximum power on the radios on the WDR3600 seems to be around a 2-3dB difference, its not a lot.
I did find on the WDR3600 that gave the best overall performance and roaming experience with the 7dBi and 2.4GHz Tx set to minimum. I got a lot better 5GHz performance in Tx and Rx and roaming still works great with 5GHz. On 2.4GHz Tx performance is fractionally better at range (only about a 5% gain), but Rx performance still shows roughly the same 20% bump at medium and long range (which makes sense, bigger antenna and AP Tx power makes no difference). Roaming works about as well as it did previously. Of course moving the darned WDR3600 made the biggest difference with a new LAN drop. Its only 5ft horizontal, but being unmasked means that in most locations on the 1st floor I experience a good 30-160% bump in performance (who knew that 4ft of cinderblock, stone and a metal pellet stove was so bad on wifi signal
).
So, anyway, extremely long story, but bigger antennas can often help some. Just don't necessarily expect a huge increase in range. Even if you get a true gain of 4dB from +4dBi larger antennas, outdoors that translates to roughly a 60% increase in range (inverse square law), but in doors you have things like walls, wiring, plumbing, duct work and furniture that all act to attenuate signal. A typical 2x4 wall with 1/2" dry wall on both sides is going to attenuate a 2.4GHz signal at least 4dB, if not more. So if you had a marginal signal in a location previously, +4dBi might be enough to turn marginal in to something that is acceptable (probably still slow). If you had NO signal before, it is darned unlikely to get you a useable connection suddenly.
I prefer to stay away from 14 inch long antennas as I like some asthetics (and my wife insists on some), so I could never do 9dBi indoors. That said, I do have an AP in my garage with the anntenas outside and I am a little tempted to get 9dBi antennas for it to swap out the 5dBi...but at the same time, I am thinking just a modest bump to 7dBi might be the way to go as I already get very good coverage over most of my backyard (whole property is 1 acre).
