Oh yes...the joy of swapping in large, heavy, components. I know that ecstasy well.
I've heard the PMC "i" line several times, paired with tubes and SS amps, on several occasions. They do sound a bit richer than the Fact line but seem to be a bit "rolled off" or focused on the mid-range where the Fact has a greater balance between the mid and high frequencies. The detail of the Fact series speakers is quite amazing.
I may be the only one to do so but I will use the Fact line as a substitute for my Aerials when listening to different amps. They are close, with the Aerials exhibiting just a bit better control of the dynamic and sustained bass than the Fact 8's do. It may be my ear or it may be that 61 liter dedicated enclosure the 10" woofers sit in, tuned to 19 hZ. I will admit that the Fact 8's have a somewhat more dynamic response at the lower levels so their "slam" factor is a bit better.
Overall I agree...this would be a very difficult choice. I've been avoiding auditioning a pair of 7T's as I wish to avoid such a quandary.
Be careful with the heavy lifting!