The DoS attacks are normal traffic, and as to the acend kill from 126.96.36.199 on port 53 I have had that from cloudflare and I'm not using cloudflare! Its more likely port scans, and the router on this firmware is a little more paranoid than usual with local DNS lookups. Those packets have been dropped but that is not a real DoS attack. A DoS attack comes from one computer normally and would knock you offline, a DDoS attack is from multiple machines. You would not just see one attack like that as a DoS attack. Lagging may be more to do with your ISP than the logs, believe me. Just google ascend Kill and you will see its common in Netgear logs.
You will always see DoS attacks in logs because you are being port scanned every day, its the background noise of the internet. Also using third party DNS servers is okay but it depends on there location and yours, your ISP ones may be a lot closer and better ironically. Also who do you trust more with the DNS logging, Cloudflare or your own ISP? Secondly you may be hiding supposedly your DNS lookups but your browser will be fingerprinted anyway so all that possible extra mileage on DNS lookups (once again depending on the location and how Cloudflare works with with CDNs (Content delivery networks give you access to say YouTube, iTunes Netflix etc from the closet server) Third part DNS servers may resolve lookups faster but cant always guarantee you are getting everything from the nearest server to you. CDNs like Akamai etc look to serve you content from your nearest location all the time. This means you may actually have slightly slower downloads and uploads, so Cloudflare could also be the source of lag and extra latency (not saying it is) just something to think on.
Anyway that's going off subject here. Basically the logs are normal, the router may be dropping packets for a variety of reasons and on this firmware others have seen so called DoS attacks from their DNS provider so maybe this needs to be reported by the team to Netgear or whoever is in charge of the firewall. So worry about the logs, I highly doubt they are the source of your lag. I would try your own ISP DNS unless they are truly awful, and look into other ways of striving for privacy on the net, and realise that no matter what you do even the size of your browser window is leaking info on you to third parties.