Your best bet would be Googling for some stalker benchmarks,
then if you don't see any that include a 4670, at least note
what the cards reviewed scored, then find another benchmark
where that card and the 4670 are pitted against each other.
It's not surprising a 7600GS isn't up to the task with
settings on high, it wasn't a very powerful card even in
it's day and now shaders make a lot of difference in newer
games. Here's one Stalker 4670 benchmark, it looks barely
up to the task.
http://www.guru3d.com/article/ati-radeon-hd-4670-review/11
While the PSU is a limitation, noise level doesn't have to
be. Taking the 9600GT in those benchmarks as an example,
at stock speeds many 9600GT can have their fan left at a
mere 20% PWM duty cycle which tends to be practically
inaudible once the cover is on the case, or more practically
the other system parts' fans are probably making at least as
much noise.