While I agree with most of what Starsmine said about latency not being a factor of Internet speed I also disagree. While almost no one will be affected by latency due to Internet speed, BACK IN MY DAY it's definitely something we had to deal with.

I feel there's a need to clarify and simplify his lengthy explanation and define some terms.
All information sent and received by computers is done so utilizing packets. Ping is the time it takes for a single packet of information to go from your computer to a server and back to your computer.
Latency is associated with ping but not the same thing and the numbers can vary widely. Latency in online games is the total amount of time it takes for a single 'tick' of a server to go from your computer to a server and back to your computer. In this case, in CS:S, you're sending multiple packets of data to the server and it's sending them back to you with each 'tick' to update your game client on what's happening in the game. The tick rate of a server determines just how much data is sent between the client and the server and higher tick rates mean more accurate onscreen action across clients on the Internet. All of this happens lightning fast, speeds incomprehensible to us really.
Because of this, it is TOTALLY possible that with low speed connections, i.e. 56k dial-up and DSL <3Mbps, you'll have a low ping but a high latency. Because your connection is stressing attempting to keep up with the server's information flowing back and forth, your latency is increased because you simply aren't getting the updates fast enough to keep up with what's actually happening on the server.
Bandwidth, which is that 'xxMbps' number all broadband connections have associated with them, is the total amount of data your connection is capable of handling at any given moment. Generally, because the data transfer required by online games is quite small, broadband connections will be unaffected by latency because the connection has no issues sending and receiving data to the server in a timely fashion. The numbers ISP marketing teams put forth are misleading however, because generally the number advertised is the downstream only - while the upstream is significantly less. Because you must also send data while gaming online, if your upstream is suffering, your latency will skyrocket because you can't send the server the data required to continue updating your client.
In short Decimate, if you aren't below that 3Mbps downstream threshold, which virtually no one is anymore, increasing your bandwidth will have ZERO impact on your ping/latency to any given server on the Internet. So there's no reason to pay more money with the expectation of increasing CSS client accuracy. The only way to do this would be to switch ISPs and it's a total crapshoot as to whether or not that will help or hurt in the goal of better latency to a particular server. In my area, one ISP is significantly better than the other when connecting to the IBIS GunGame server, for what it's worth.
I think the issue we're all dealing with on the GunGame server lately is it just that it needs some tuning up. The last couple of weeks have affected me the same as you, I've been knifed from incredible distances and shot dead around corners regularly. The explanation for this is simple - my client and your client aren't seeing the same point in time from the server. If it's happening to just one person, this is usually a client side issue, but with as many folks as have been complaining lately it's no doubt on the server side.
And I think the server is located somewhere in Virginia or D.C. An IP address look up would help you pinpoint if you're really curious, just plug the IP into Google and it should pop up easy-to-read results.
Hope this helps!