Experiences with HP aC++ or Sun Studio C++?

I'm considering different platforms and compilers for a project.
Anyone have experience (positive or negative) with HP aC++ on HP-UX?
It seems fairly standard compliant since it supports Boost 1.34, but
I'd like to hear from you all. Same question for Sun Studio's C++
compiler on Solaris.

I gather from http://hpux.cs.utah.edu/hppd/answers/4-4.html
that
running g++ on HP-UX is not particularly efficient, but apparently g++
on Solaris works reasonably well (at least version 3.x that comes with
it) .

Any experiences related to standard conformance or efficiency that you
could share would be helpful. TIA.

Cheers! --M