Unfortunately the uses of a consumer router to limit a DoS attack are pretty useless. Too easy to simply flood out a cable/DSL line. However it can easily stop other attacks that depend on hitting a certain port on a computer in hopes that an open service can be exploited. The router simply doesn't forward incoming connections unless you've specified the port should be forwarded, so you're automatically protected from many worms. However, you're still susceptible to email worms since those are activated behind the router, and your machines would then be used to attempt infections of other machines. Only a virus scanner can prevent that (or simply being vigilant about what's done on the computers).
The ProSafe line seems to be more business-oriented than home user. It does have Stateful Packet Inspection (I assume you meant SPI not ISP), which is nice, but not an absolute requirement or going to make a huge difference for your uses; when you're behind NAT, nothing's getting past the router to affect your machines, and SPI simply prevents the router from being overloaded trying to process invalid traffic. You think you're going to piss anybody off enough to make them specifically attack you? (Attacks that SPI would hinder are all specific attacks, not a worm spread type.)
You can get the RP614 WebSafe router for about 20 dollars less, which provides all the functions you need, including logs of browsing activity that can be emailed to you regularly. The ProSafe doesn't mention being able to log browsing activity.
Any router with "parental control" or "safe" mentioned will have features such as URL blocking either by specific URL or by keywords. Unfortunately a router can't be used to filter a broad range of sites based on content (applications like NetNanny can be used for that).
Internet gaming shouldn't be affected at all with any current routers. Most games don't require an inbound connection to be made anymore, and the few that do can be fixed by configuring a port forward. Mostly older games have issues with sharing a single IP while gaming or issues behind NAT.
