I happen to be a long-time fan of Boston Acoustics, both home and car. I had a pair of the Rally series plus a pair of their stand-alone tweeters in my last two cars (transferred from one to the other), combined use of probably 12 years, and they're still working fine, although I'm not using them anymore. So they're durable.
I would say spend a bit more and get the components (SL) rather than the coaxials (NX). Listen to both of them and make up your mind which sounds better and is it worth the extra cash.
The Boston SL60 6.5 and the Kappa Perfect 6.1 cost about the same ($220-$230 a pair), so the key is to audition both of them. Best is to do an A-B listen in a store, then buy them online if the store won't match the above price.
i had nx67's front and back and they sounded great but i had two problems. Something about the neo. mags on them seem to heat my amp up much more than the rc620's i replaced them with which brings up prob 2 (why i replaced them) with only throwing 75rms to each of the nx67's i blew two of them not good so i switched to rc620's and couldnt be happier i crank these babies all day no prob great for the money