I personally do not know about render target and Octane 3dsMax in the future.
The slowness you report has no relation with ORC or SA export, file creation process is the same.
I think your issue is caused by where you're saving .orbx,
something like external hard drives, hard disk paging system...
Try to modify your saving path; Octane 3dsMax generally exports to C:\..
this could slow exports because other applications (or OS) are using C:\
Win 7 / i7 5930 - 32gb / 1 x quadro K620 / 2 x Evga Titan X Hybrid