Both speakers are personal favorites of mine, but...
If you were to chose a tube amp I would probably suggest the Tannoys over the Pro Ac - but it really does depend on the tube amp as well. The Tannoys are more efficient at 93 db vs 89 db for the ProAc
Otherwise I might suggest the Pro Ac, because the Tannoys can be a little picky when it comes to placement (i.e. toe-in) and they like a larger room.
I love the Tannoy in a large room with lots of space around them - e.g. they really excell when there is 4-5 ft from sidewalls and 6+ feet from the wall behind them, but I think the ProAc can be more versatile from a placement perspective in a smaller space.
Also, Tannoy requires toe-in such that the axis of the speaker crosses just in front of the listener - this can vary from model to model (you probably know that). With ProAc the toe-in is room dependent, but not as severe as the Tannoy
Either will provide superb sound quality - as you know the Tannoys tend to be a little smoother and relaxed. Diana Krall really does sound velvety on Tannoys
The ProAc are a different sound - great, but just different
Also it depends on you musical tastes
I think since you own Tannoy now - I would recommend the Prestige Turnberry GR Limited Edition. You know the "Tannoy sound" - changing it may not be to your taste.
If possible - listen to them both with the same gear in the same room
My last speaker purchase - I took my amp and speaker cables to the store - SOLD!
Trust your ears - Steve :-)