The update SHOULD apply otherwise.. problem is, you cant easily check, when not in bridged mode :(
This is where router providers, are REALLY pissing me off..
Your 820L... Dual band, AC1200 (so not the newest AC, but still AC, so a step up from N only)... overall a decent router.
BUT WAIT.... 10/100 ports ONLY.
Really.. even the MAX 300Mbps on the 2.4 frequency???... ONLY good for between device to device then.. since they have neutered the wan port at 100.
In the end, you would never get your MAX plan speed, through it. Device to device.. your fine.
Maybe see if you can re-sell your old one, to someone who isnt on as high of a plan.
Either of the two you posted.. have 10/100/1000 ports.. so should be fine. Really in the end, would be how much you want to futureproof your setup (AC 1750 is newer than AC 1200....they even have AC1900 now).
PERSONALLY i cant vouch for how well those routers work.. how the processing is in them, etc.. (i have had BAD experiences with dlink in the past, so tend to shy away from them now personally.)
You would be suprised though, how the RIGHT router, can make a difference.
I am on the 30/5 plan. So a 10/100 router would be more than good enough, thats what i used to have, an linksys e2500. Was pretty fine, got 23/4 on it wireless.. so was pretty content. (allthough with wired, speedtest could get 35/5, due to speed boost).
Wireless range, due to the built in antenna.. missed a few corners of the house.
So went with the ASUS RT-N66U. External antennas, so gets MUCH better range. 10/100/1000 port.. but for me that shouldnt effect speed, right?
Just the PROCESSING POWER of the router itself, is night and day. I actully can pull the same if not BETTER than a wired machine sometimes via my wireless.
Other models to consider (but may be a little higher $$)
Asus AC Models - All are well reviewed, but pricey
Netgear AC Models - I know a few with the R7000. Best pricepoint AC1900 router out there, and works very well.