While it is true that CAT5 runs at 100Mbit, CAT5E (which Sentinal installs as standard) supports gigabit and would be more than enough for a home network. The real benefit of CAT6 technically is that it supports 10gigabit - so is more future-proof but it will be a long, long time before 10gigabit speeds are needed in homes.
Although CAT6 is not that expensive to upgrade to I couldn't see any real need. My opinion anyhow.
You might also like to know that Sentinal also run CAT5E cabling to install telephone points - they just physically connect 1 pair only. This means that conversion of telephone points in the house to full data outlets is not too difficult to do after your build if you know how. I certainly took this into account when positioning our data and phone outlets around the house.