Agree. I am concerned you are already sometimes listening near the top of your amp's volume range. Running valve amps hard reduces tube life.
You don't mention which PMC speakers you are thinking of buying. As you are using tubes it is worth looking at their impedence curve to check it is not near or below 4 ohms over too much of the frequency range. If it is, this will put more pressure on the amp even if it has a 4 ohm tap you can use. Some PMCs are a benign load - the fact.8 don't go much below 6 ohms.
One other thing you need to watch out for is over-optimistic sensitivity values quoted by manufacturers. Whilst no two tests can produce identical results, in 40 years of reading John Atkinson's tests in Stereophile I have never found his sensitivity measure to be higher than the manufacturer's figure. His measure averages 2-3dB lower. I have seen manufacturer quotes up to 6dB higher. It pays them to publish the highest figures they can as we all want more sensitivity.