Hi,i just setup Focusrite saffire pro 24 interface buffer size at 512.i have one instance of halion sonic se on 2 midi channels,sylenth1,and a reaktor 5 user synth.
a few effects,nothing that should put too much drain on my system
i am gettin cpu spikes,and can hit 50% on the meter sometimes.
AMD Phenom II X6 1090T Processor 3.20GHz 8GB Ram
surely i shouldnt be crackling.
Apart from giving my usual advice of making sure Steinberg Audio Power is on (in Device Setup, always necessary in my experience, regardless of what else may be too), I would browse around for Reaktor and NI in general. Seem to recall a few fingers of suspicion being pointed in this direction too. Try this post: ASIO spikes - Cubase - Steinberg Forums
thanks for reply,i have went through device setup,i dont see any steinberg audio power setting.im using cubase 6 latest update
my apologies i see it now.
i got the message about power consumption.
why would it be a worry?
That Focusrite is a firewire interface yes? Are you using Windows 7? I’ve read a lot of talk of buffer problems with the solution being to roll back the Windows firewire driver to the Legacy driver:
http://www.focusrite.com/answerbase/en/article.php?id=1030
Rev.
Devices - Device Setup - VST Audio System, bottom half of dialog. And watch it, it can reset to OFF as I have just this very second discovered 
(Just for the record: this must be due to a crashes I have been suffering today since updating video drivers, which made the mixer windows resize themselves.)
Although even my ancient Focusrite SaffireLE has been working with the non-legacy drivers since FR updated their drivers some time ago. Yours is more recent than mine, right? Certainly used to be an issue, though, which is where I presume Rev has picked this up from.