The only information I can find (on the forums) suggest a 200GB limit.
It is still not easy to get to Xilo's FTTC pages. ADSL 24 is slightly more expensive, but with NO limit at the present. I like the freedom that that provides.
But, with the extra speed and all the content out there, 200GB can be used in a beat of a humming bird's heart
As I said, you will be in very good hands with either company.
Stress - the condition brought about by having to resist the temptation to beat the living daylights out of someone who richly deserves it.