Which amp would you choose and why - Pass Labs XA-25 or First Watt F8?

Both are rated 25W into 8 ohms, but the XA25 is 50W into 4 Ohms and the F8 is 15W into 4 ohms...and many 8 ohm speakers still dip at times to 4 ohms or less...I think overall the XA25 is more powerful...many of the reviews of the F8 seem to include a comparison with the XA25...I loved the F7 with my Avalon Ascendant II speakers in a small room...

I havent listened to the F7, but have the XA-25 paired with a Cary preamps (SLP 98 and SLP 05) driving Spendor D9s (90db, 8 Ohm) and Chapman T7 (89db, 4 Ohm).

The Cary preamps and XA25 have amazing synergy in my system. The XA25 may only be spec'd as 25W but it sounds more in command of my speakers than the Rogue ST100 that I owned.

 I considered both these amps and even asked Reno Audio for a F8.  He told me to get a XA-25.  Said it was a better amp all around.  Took his advice and love it.  I have paired with an XP-10 pre and Salk Exotica monitors.  Wonderful, I have no desire to change it.

The XA25 is the much "safer" choice in that it has much more power and is stable down to 1/2 ohm.  From everything I've read (and I had the XA30.8 paired with similarly spec'd D7's), the XA25 will have better bass and silkier mids.  The F8 may sound a bit more agile but possibly lean in comparison. Your Tannoy's can go as low as 20hz and the impedance dips all the way down to 2.9ohms at 100hz.  I really think you will need the XA25 to drive those Tannoy's properly.  What amp are you using now?