Does it transfert the task to the video card?
No, a better video card won't help you much. LR doesn't yet use GPU acceleration.
There have been many threads and much discussion here about slow performance in LR4 and the general consensus is that CPU performance makes the most significant difference*. You need fast clock rates and as many cores as you can afford.
Dual core Xeons are getting quite old in CPU terms now and depending on clock speed may(will) be significantly slower than contemporary CPUs.