Act-3D and the staff here on the forum, of course can not make recommendations regarding specific brands, but some forum users may want to contribute their personal views and experiences.
In any consideration of a PC/laptop, please give due consideration to our hardware guide on the forum at LUMION 3: Minimum hardware requirements
, and the official info on the Lumion web site - Specifications
Also, each new version (and updates) can sometimes provide more features that may have a cost of additional processing to run, for example the soon to be increase in Reflection Planes in Lumion 3.1.1. This means then that like all things, the more power you can get for the budget or if you can extend the budget now rather than in future, the better off you should generally be.
This question would best be responded to by the technical support of the CPU hardware you have (local HP resellers/support).
The NVIDIA GTX770 reports on the net indicate a good performance card, although oyu might want to also consider the GTX780 (but costs more).
The issue with matching new and old hardware is always going to be:
1. everything runs at the slowest speed
2. age/hours of use of older hardware - how long before likely fail.
Morten: "if the CPU isn't fast enough, it will act like a bottleneck which prevents your graphics card from operating at its true potential. In practice, the result of a bottleneck is a lower framerate in Build mode."
It is not just the ability of the CPU, but also the question of the motherboard to support bandwidth. The speed from the new GPU's is in part because they support higher bandwidths, you will not gain from this due to the limits from the motherboard.
The new GTX700 series supports PCI-e v3 for faster throughput. However not all CPU's (even some new versions) support this platform, so again, the system will not run at optimum.
I myself have an Intel Core 2 Quad Q6600 @2.4Ghz. The motherboard and the CPU are the key reasons I chose to not update the GPU from a 560 to one of the 700 series. Too old, too slow, no benefit. But that does not say it would not work and be faster, just not optimised or anywhere near a preferred medium or longer term option.
At end of day, budget will also limit choices.
Please search for recent topics on:
1. bottleneck - discussions around CPU's limiting the throughput for the graphics card
2. PCI or Intel or Bridge.
Here a couple of topics covering some of the above:
1. PC's With GTX 780
2. GTX Titan on a pci express 2.0 board
3. Benchmark Results (v3.1.1+)