If the two partition files are on the same storage volume in the virtual server, no performance will be gained, but if you have software installed on the system already you won't have to reconfigure things by keeping it as it is.
If you move the virtual files to different storage volumes on the virtual server then you can gain some performance, theoretically, since it would come from different hard disks.
In reality it also depends on your system load. If your system will be lightly loaded then you're going to be investing a lot of time on something that will yield only a tiny performance gain at all.
Your best bet is to just virtualize it and test it, see if performance is acceptable under some test conditions. If you don't have anything on the D: drive, just make one big C: partition.