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I've seen 11.4V-11.8V straight off the charger with NiCds, but speed ain't about voltage, it's about current & how much of it you can deliver in 1 lump without affecting the voltage too much, which is what high quality LiPos are supposed to be good at. eg it's all very well having an 8.4V pack at your disposal, but if it can only deliver 1-2A continuously, it's going to be worse than a 7.2V pack delivering 10A.
The other thing to take into consideration is the voltage-drop when it's delivering large amounts of current (Typical of tired batteries) - it may be a full load will cause 10A to flow, but if this causes the voltage to drop to (Say) 5v, the overall power delivered to the motor isn't as good as it could be with a healthy battery.

If you want to get a good idea of how good a battery is, put it under a lot of load & measure the current flowing AND the corresponding voltage at that load (DC Power = volts x amps). Ideally you want to be able to supply all of the current the motor requires without dropping the voltage - the battery should be a "lake" of power, not just pressure built-up behind your thumb over a hose-pipe which disappears as soon as you try to use it

If you measure the voltage across a flat battery, it's not that low, I've seen 6-7V on NiCd, dropping to 0.3v or less as soon as you hook it up to a load. If you then remove the load, you will see the voltage recover slowly back to the 6-7v