Based on the old MTS Lighting Bolt and Lighting Max plans I think we have the following:
Max DSL speed on a single line with ideal conditions is 32 Mbps.
TV bandwidth requirement (estimated) 7-15 Mbps.
This means a pair-bonded connection has a theoretical maximum of an estimated 64 Mbps, however some of that is lost due to the bonding overhead.
Add in the allowance for TV space and we arrive at close to the 50 Mbps of Lighting 50.
Keep in mind that there is additional overhead on the Internet connection which will reduce your top end speed.
Ultimate TV service can have 0, 1, 2, or 3 channels on at once, and by "on" that includes PVR recording. Each of those channels can be SD or HD, with HD reducing available bandwidth more than an HD channel.
Based on these observations, if you want to test your maximum connection speed, first max sure all tv channels and pvr recordings are off. Also, if you absolutely need to have some tv on and still achieve the highest bandwidth possible try to limit it to a single SD feed.