The whitenoise you usually hear in the upperranges when trying to make a supersaw, which i have diligently tried to do for some time, is because of low (unacceptable) khz sample quality, such as 48khz, or even 96.. you have to go all the way to 192 to really make it inaudible on a (digital) VSTi.
In theory the sound should be clearer and more "desirable",
and MY GOD, it was. the sound changed COMPLETELY, in a good way
i could render out the difference, whereas render1 in 192khz and render2 in 48khz, but whats the point ->
However, cpu usage increases exponentially, and so youre back to the good olde render to listen era
i bought my quad core ~10ghz (FL8.5 supports multicore, 2.8ghz per core) for this same reason, to not be annoying when making music
needless to say, it was a shock to see cpu make a hyperjump
i also learned that 11 unison voices is a good maxima for supersaws in general, 10 should suffice
I dont know if theres anything you (karmafx) can do to optimize for this kind of thing, because its natural that exponentially more work means exponentially more cpu usage
but you should take a look, if youre able to produce 192khz
in any case, it was a real pleasure listening to my instruments with this highest quality available (my soundcard supports it too so!)
Other than that, is there any way to overcome this? such as hardware related
Verdict: It's serious business.
If available, don't get intimidated by having to render previews.
At least you should be able to play one instrument at a time and freeze the others.
I suppose that analog synths (sometimes) are of an un-resonant nature because of inherent cycle "flaws" caused by (such as) copper wires,
which makes the cycles not interfere as often, if ever, generating unique waves pretty much always. Prevents whitenoise? Probably
(I also believe you can get 192khz without any mentionable cpu loss from them either way)
(btw: Havn't we been over this before? 
)...but weird?! 
The code they use is 99% the same.