Probably not significant. But why do you need it? Netflix doesn't need high speed. To stream BlueRay 1080p from a server to the TV? Does the TV even support 1080p via ethernet/WiFi?
More common 1080i doesn't need really high speed.
If you must, get a cat5 cable to the TV by PITA means.
It could be. The question is, what is your situation now, or what is the theoretical situation?
A 5GHz connection and 5GHz is viable/faster than 2.4GHz? Then, yeah, it is possibly a lot faster.
5Ghz 11n vs 5GHz 11ac, both 2:2, my speed increased from around 90% on the low end up to about 140% on the high end moving from 11n to 11ac.
2.4GHz, minor differences in comparison...but its still the same old 150Mbps per stream at 40MHz link rate (I don't have 256QAM/200Mbps per 2.4GHz router or client), so any differences are up to better processing power/radios/etc, not protocol.
That said, even with the huge increase in speed for 11ac, outside of line of sight, the performance difference between 2.4GHz and 5GHz with my 11ac equipped laptop and my AC1750 router starts dropping percipitously.
Line of sight and close in, I get on average >55MB/sec on 5GHz and >28MB/sec on 2.4GHz. Once I hit what I would consider medium range for 2.4GHz, I am down to maybe 16-18MB/sec on 2.4GHz and I am still at around 20MB/sec for 5GHz...so faster, but only by a relatively modest amount. long range, but not extreme, I am down to 1-3MB/sec on 5GHz, but 2.4GHz is still going decently strong at 7-9MB/sec. Get to extreme range for 2.4GHz and 5GHz can't even be seen, but I'll get around 3-3.5MB/sec on 2.4GHz.
So...what is the use case? Are you in the same room as the router? Maybe one room over? If that is the case, you'll probably see a big improvement going to 11ac, even against a good 2.4GHz 40MHz connection with no interference (and 2.4GHz just LOVES to be interfered with). If the distance is high between the router and the smart TV, but a 5GHz is still viable (As in, you can GET a connection), then odds are decent it'll be a lot faster 5GHz vs 5GHz...HOWEVER, the improvement over 2.4GHz at that point is likely to be a lot more minor, supposing 2.4GHz isn't just faster (in which case 11ac router and dongle are likely to buy you nothing).
The huge improvements that 5GHz saw with my move to 11ac now means that 5GHz performs better than 2.4GHz 40MHz over roughly 80% of the coverage area that I care about in my house (the areas I don't care about, are covered by my 2nd access point, which is an 11n AP). On 11n, 5GHz 40MHz was ONLY faster in the same room as 2.4GHz 11n (and by a smidge, like 5% faster). Compared to 2.4GHz 20MHz, 5GHz 40MHz was only faster over about half of the area I cared about...and that is less than half the bandwidth capability line of sight for 2.4GHz 20MHz compared to 5GHz 40MHz (in theory anyway).
I am very much looking forward to replacing my 11n AP with an 11ac AP as that should mean that 5GHz is faster over my entire house and not just most of it (well, there might be a room where 2.4GHz 40MHz might be a smidge faster).