I shoot 55gr. almost exclusively, but I am aware of the direction some of the newer loads are going (heavier).  1/7 would of course be better for some of the experimental rounds we've been reading about, BUT, in the meantime, does the 55gr perform equally well in 1/7, in comparison to 1/9? Is 1/7 equally as accurate, or acceptably accurate, or seriously impaired? I am talking about accuracy outside 100 yds.  Considering a barrel purchase right now.

Shoots fine.  Regardless of the outcome of the military testing program you're not going to see heavier/longer bullets in 5.56mm at affordable prices for several years.  I'd not pay a premium for 1/7 right now but if the price was the same and it was chrome lined why not?

-- Chuck