Haven't heard that particular 6SN7, but they're much cheaper here:
Rockadanny, The tubes in the link you provided are Sovtek, rebranded as Tung Sol.
New Sensor bought rights to Tung Sol and Mullard brand names a few years ago to add credibility to their Russian made tubes. Genuine Tung Sol are superior, provided they are not defective or worn out.
Here are some wonderful 1940's premium Tung Sol (real thing) with less than 20 hours left to bid at Ebay.
Real Tung Sol Ebay
And here are some at Audiogon that look nice
Tung Sol Audiogon
I have no experience with your preamp, but I have a lot of experience with original Tung Sol tubes, they are some of the best made of this type. If you don't like the sound in your current piece they can be stored for another brand you may own in the future.
I have about 40 of these in my own tube collection along with RCA 5692, my other favorite that would work in the same place in your preamp. They are not making these any longer, they will continue to increase in value and are always good to have around.