Most ping tests use very small ping packets. They simply show round-trip time to and from the pinged location. The test does not show packet loss. If, during a market day, your link experiences packet loss, your effective link speed decreases. This is a result of the TCP/IP protocols the Internet uses to provide us with connectivity.
A typical ping packet may be 32 bytes. Depending on what you are sending/receiving from your trading/charting platform, your packet size will easily be 10 to 20 times larger. If there is a problem (noise, congestion, route switching, etc.) and the packet is detected as bad, the TCP protocol will detect the problem and request a resend of the bad packet. This holds up any good packets until they can be properly recombined. Thus, "packet loss" adds delay to your transmission time. It is far more noticeable using "real" packets than it is using ping-sized packets.
You don't exactly say so, but you appear to have both cable and DSL running now. If this is true, then before making your choice download the free version of PingPlotter (
www.pingplotter.com). Run it during trading hours on both the cable path and the DSL path. Look at the path graph and note whether there are any numbers appearing to the left of the individual path segment ip addresses (column is labeled PL%). Those numbers are retransmissions (lost packet) requests. Also look at the graph. The individual plot points should have no (or short) horizontal lines associated with them. This is the path variation for that leg. No line is good. Long lines, bad. In interpreting the line length remember that auto-scaling is used. If you really want to invest, pay the $30 for the paid version of PingPlotter. It adds another graph at the bottom that shows packet loss over time.
Lots of transmission speed doesn't really help if there are a lot of retransmission requests going on in the background. Depending on the number of quotes you receive (and your vendor), the greater speed can help keep you up to speed with the market during very busy periods.
If your computer is able to receive and process (or locally buffer) the info from the vendor's server very rapidly, the vendor's buffers don't fill up waiting for you. If it can't, your machine must play catchup. This is not true for InterActive Brokers. Their quotes are essentially time-sliced (sort of sampled so some quotes/trades may be missing, but the amount of data transmitted remains constant and current during busy periods). Thus for IB, gobs of bandwidth (transmission speed) is not necessary. But - packet loss is a problem for either approach.
Have fun,
Jack
