Anthem Pre 2L tube rolling question

The Anthem Pre 2L uses four matched 6922s. I've swapped in plenty of varieties, and now have found some that sound really good (Valvos) but were pretty expensive. I've been swapping whole quads in and out.

Is it ok to use one pair of "good tubes" and one pair of stock tubes (or other ordinary tubes) in combination and still get positive effects? Of course, this way my quad of "good tubes" will last twice as long.

Just curious - of course I need to know if the good pairs should be on the front or the back.

Anybody with experience on the Pre1L or Pre2L can answer?