@Wodin, the gpu part refers, as far as I know, to physical cache for video memory (your actual vid. memory that is reserved for the simulator in this case). The vir number is the virtual cache, which, generally speaking, is the gpu video memory being used by the sim. that has already been translated into virtual vid. memory.
Both physical and virtual vid. memory are used by programs - but the vir memory is a bit faster to access since already translated/paged to a virtual space. The gpu memory on the other hand first undergoes paging/writing to virtual space and is then accessed. When you add up the gpu and vir numbers that you have given in your example, the sim. in that instance had access to about 5310 MB total GPU memory (physical memory), with about 1765 or so MB of that batch already being translated into virtual space, and leaving about 3545 for the gpu (physical) space.
From my various tweaks and iterations of the WOFF GPU Tuner Patch, I've noticed that the gpu number is not that crucial to performance/FPS - it can range anywhere from 2000 to 4500 approximately and there is not much difference. The vir number, on the other hand, should remain above 1100-1200 or so - otherwise there is a slight performance drop of about 10 FPS on average. These are things that I noticed on my rig. when tweaking the tuner patch - results may vary depending on rig. setup.
GPU and IT specialists are of course welcome to pitch in with more info. if they wish to append/correct things to my post - my explanation above is very general. As Pol says, the numbers are fundamentally unimportant to the end user.
Happy flying all,