As the title says.
The slowdown is randomic, but HUMONGOUS (10-100X).
Think of RTT: both the vray FB and the max ones come up, and the moment i close the max FB Vray picks up speed.
Rendering within the max FB is just slowness™ guaranteed.
It may have been fixed already, or not be a Vray issue, but i thought i’d flag it.
Do you have the 3ds Max bitmap pager enabled? Do you have the light cache “show calc phase” option enabled too?
Best regards,
Vlado
neither, nor.
Then I have no idea 
Is this on any scene?
Best regards,
Vlado
Actually, no.
I was doing some performance profiling for a noise analyser script (yeah, i’m still on that one…), and out of laziness i was using the max FB, getting the oddities in performance with a plane and a domelight.
Given i have a 24 cores beast, with the latest and greatest of Intel’s chipsets, i thought it may have been an issue with memory mapping (non-SMP), and god knows what else…
Changed every possible relevant bios setting without results, i even got a different workstation, which seemed to work at the IT desk.
It got back to me, and again it was slow and erratic.
The moment i used the vray FB it all stopped misbehaving.
Rendering to texture opens a max FB by default, even if the vray Fb is active, and that’s when i noticed that the slowdown (which is, incidentally, growing the more vray renders: it starts at normal speeds and slows down more and more as the render progresses) would disappear the moment i closed the max FB.
It could really be down to an odd hardware combination, but i’d have to confirm this (i’ll grab someone’s older workstation tomorrow).