There's no one answer to your question I'm afraid, we can't know what else your computer is doing in the background. Xara may not utilse multi core (for example) but your com isn't just looking after Xara.

Xara - 'hey, give me a CPU to use' multi core processor - 'sure, use this one, rest of the team carry on doing the other tasks.'
Dual channel RAM. Xara - 'hey I need some RAM' multi channel - 'sure, read with this channel, write with that one.'
NVMe. Xara - 'hey I need to save all this work' - NMVe - 'sure, I can write at about 1,500MB a second'

If you're just thinking about Xara, then RAM and an SSD would be your best bang for bucks, but it isn't the whole story. Sorry to be the bearer of disappointing news.