pushf v rcl, save, restore carry flag

I'm writing my own large integer library in x86-64 assembly, and, to
start with, I'm working on addition. My basic approach is to loop
through each pair of 64 bit longs and adc them. The one thing I've
noticed is that for this to work I need to save and restore the carry
flag, as, my loop counter sets it too. What's the fastest way to do
that these days? I'm looking at pushf, popf, but, some sites that
I've looked at claims rcr/rcl ought to be faster as of 486 and
pentium. Is this still true?

I'm looking at the AMD64 Architecture guide, Vol 3, and it doesn't
give much about timings at all, although it describes the instructions
reasonably well. Is there a document out there that gives some sort
of an idea of clock ticks for instruction (like the old days), or is
it that today's processors are so massively pipelined that going by a
ticks per instruction isn't going to cut it and you really need to
think in terms of everything else you have going on?

.

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