Definitely upgrading my graphics card (HD 5770). Not sure whether to go for an nVidia or an AMD - AMD seem to do better in Arma 2, but Arma 3 is being developed with nVidia GPUs, it seems, which may mean that the situation is reversed. The Alpha should tell us. Won't be upgrading until HD 8000 series/GTX 700 series anyway. Also, depending on just how CPU intensive Arma 3 is, I might get myself a new motherboard for a Haswell CPU (currently running an i5-2500), which should also open me up for a SATA-3 SSD. Can't hurt to step up to 8GB of RAM either. I'll probably do all this over the next few years anyway, but Arma 3 may well accelerate the process considerably.