You are not the target of a DOS attack. A couple of ping packets and 1 or 2 scans over TWO DAYS is nothing to even be concerned about.
If you are having performance issues it is either due to your line being crap (IE Speak to your ISP) or your internal systems are misconfigured/infected.
A DG834 is not a high performance router, it will not handle huge amounts of connections. You have probably set up your torrent client to use massive amounts of connections (IE anything more than 300 is too many) and your net WILL BE UNUSABLE while you torrent.
If you are having issues on another system, while not doing anything (Be it torrenting or otherwise) then get your line checked out.
Also - What is all this crap about Netgear Firewalls being bad at blocking legit data? It's a firewall, it does not make opinionated choices. It does what it is told.
A firewall is not going to cause HTTP browsing performance issues "just because".