CFLAGS for certain ports

Hello,

New to FreeBSD and first post. If I got the wrong mailing list, just
let me know where to ask my questions.

I would like to see how well FreeBSD does as a workstation OS in the
HPC world due to its stability and reliability, as well as LLVM/clang.
I would like to know if FreeBSD has something similar to Gentoo's
/etc/portage/make.conf file and /etc/portage/package.use/* files in
order to compile certain ports with certain compiler flags. Currently
I mainly use CFLAGS="-O2 -pipe -mtune=native" for most of the
applications, so nothing really aggressive (in general).

I've been reading through some FreeBSD docs (Handbook and ports
documentation) but haven't found the answer (maybe looking in the
wrong place).

Regarding LLVM/clang, I've been reading the documentation and found
these flags: -arch=<whatever>, -march=<whatever>, -mcpu=<whatever>,
--target=<whatever>, target-cpu <whatever>. I'm not quite sure which
one would be the one to use. In case someone wants to know, my initial
play/test machine has this processor:

CPU: Intel(R) Core(TM) i7-3820 CPU _at_ 3.60GHz (3600.11-MHz K8-class CPU)
  Origin="GenuineIntel"  Id=0x206d7  Family=0x6  Model=0x2d  Stepping=7

And I'm currently running: 11.0-RELEASE-p8.

So I imagine I should use something like CFLAGS+= -march=corei7-avx
-march=sandybridge -target-cpu. Is that correct?

Currently all our deployed workstations are Intel with NVIDIA Quadro
graphics cards.

My target is not to migrate everything, I just want to know if FreeBSD
would be suitable and where.

As I mentioned, this would be for specific scientific applications,
not system wide.

Thanks !!