Well, today I found out for sure that there is no real correlation between signal strength and download speeds. A few days ago I noticed that my signal strength light had turned blue (which is good) and the router status page showed something like -81 dbm which is the strongest signal I've ever had. Upon running some speed tests I found that there wasn't any significant difference or improvement. Bandwidth was variable as usual and averaging around 1-2 Mbps down and 1 up.
Now, today for the first time ever I noticed my signal strength light had turned yellow (never seen it yellow before) and the status page showed -101 dbm. A quick speed test resulted in the fastest download speed I've ever had: 3.67 down and 0.89 up (usually my upload speeds are actually faster than my download speeds). So clearly the performance is actually limited by the systems they have in place at the cell towers and/or the local cell traffic load. I now see that my signal strength light is back to its usual green status with a strength of -89 dbm, which is about what I usually see.
I think the best way to monitor your performance is to simply use tracert and watch the packet transmission times. When things are really good all the times I see are below 100ms. When things are really bad you see some complete timeouts "*" and/or times up aroung 3000 to 5000 ms (3-5 seconds) which is horrendous. The problem is that seeing the numbers doesn't really help you since you have absolutely no control to change or improve them. The only control you have is to call Bell and complain when you're getting really bad performance.
I have to say that my average performance has improved over the past couple of months, so consistent calls to Bell regarding the problems does seem to help. They never call us back to tell us that they did anything so we can only guess and assume that they're trying to make it better. It's still hit or miss though when it comes to watching videos, listening to online radio or using voice apps like Skype. This can be frustrating.