Something you might need to watch out for in the gaming and developing situation for you Virtual Worlds work is OpenGL versus DirectX support in your video card. If your developing C++ against the Source engine using Visual Studio - no problem. If you are using Unreal Editor, Hammer, Radient, or one of the other 3D world builders - then this applies.
The situation is that most, though not all, games on the PC favor the DirectX for display at run-time - a few favor OpenGL and a few support both but most favor DirectX. So, to run a game (your virtual world) you want good DirectX support in your video card - especially as your world gets very complex with lots of effects.
However, many of the editor tools use OpenGL. So, to build really big levels and navigate them smoothly, you want a card that is great at OpenGL. There is an paradox here in that even games that favor DirectX at run-time may favor OpenGL at design time.
Sadly, this is a differentiated market - e.g. Nvidia cards are either good at one or the other - so you have to make a choice of some kind and pick which is more important and buy/install the card that best suits that decision.
In a desktop PC, some people put both into their PC and run a multi-monitor setup. If you do this, remember that DirectX (the run-time environment) will go to the primary monitor so use the DirectX card there. This is a handy setup because you can walk-thru the run-time of the world on one monitor while navigating the same world in your design/builder tool on the other monitor. This is tricky though because most motherboards can only take one video card or getting two video cards in a PC is, at least, tricky. It can be done but takes some research, planning, testing and patience. You can also run into other bottlenecks in the bus, CPU, memory, etc.
If you favor laptops, your choices are more confined. Dell for example makes some very good DirectX laptops (the XPS line) and some very good OpenGL laptops (the Precision line) but there is no swapping video cards in laptops so you have to make a decision on the whole machine (CPU, screen, etc.) based upon OpenGL/design-time versus DirectX/run-time.
The OpenGL/design-time versus DirectX/run-time paradox doesn't apply with every engine/tool combination so check into your preferred tools and you may find this doesn't apply.
There is also a question of degree here. An XPS isn't optimized for OpenGL but it is a darned fast machine and renders OpenGL might well - the converse is true of the Precision (drivers for DirectX aren't great but plenty good enough).
The breaking point is probably not if your video card doesn't run well but not at all - some aren't supported by DirectX and some don't work with OpenGL. As long as your card isn't incompatible, any decent PC or laptop will probably run it well enough to for most purposes. In this regard, I have to favor the DirectX side of the equation - especially on laptops. Many games/engines list specific cards they support and those are the mainstream ATI and Nvidia cards - sometimes not even the laptop variants. So, those games/engines may not run with your OpenGL workstation card. Conversely, while some of the tools are OpenGL and some of those don't work with DirectX, this is more rare. This is especially true of OpenGL laptops that are often purchase by companies to support a specific application (e.g. AutoCAD) and care not a wit about support for DirectX and the associated game/engines.