The spec you listed works out to just over 10dB of gain (Log(6.5/2) * 20). IMO this is about the amount of gain a preamp should have. With a Zout of less than 30 ohms this should be able to drive most amps nicely.
Many power amps have between 20 and 26dB of gain and need between 1 and 2 volts to reach full power, some more and some less but many are in this range. That should match up very well with your preamp. Even amps with say 30dB of gain shouldn't be too bad though the volume control will be more sensitive. At one time I had a preamp with nearly 20dB of gain and a power amp with somewhere around 32dB of gain, that was not a good combo in regards to the usable range of the volume control. It was very loud by the 9 o'clock position of the volume knob.
mike
