backport-concurrent vs. concurrent-1.3.4

Hi -

I've been using util.concurrent-1.3.4 for some time and recently
discovered the backport-effort. Just as in JDK 5.0 some rather handy
classes are missing compared to concurrent-1.3.4 and I was wondering if
there are any recommendations for or against either one? I very much like
the stress-testing and the backport's obvious ease of forward-migration to
5.0 (if that becomes a requirement one day) but so far had nothing but the
best experiences with Doug Lea's classes. Also, quite a few OpenSource
packages have adopted concurrent-1.3.4 and just mixing things - while
technically possible - is IMHO not desirable. Any wise words for or
against  either one? The backport docs unfortunately do not talk about
this (or did I miss it?)

Thanks for any insights -
Holger