RA's have to be section 28 compatible - which means a max of 75% in equities. But many are conservative balance funds - so some have less. Then you have management fees. That said, have heard of a Sanlam RA that has 75% equities and 25% listed property.
Of course, you do score with the tax, depending on your tax bracket, anything from 18 - 41% - a huge plus.
Personally, if I earned a decent salary I would make sure I maxed (15%) my RA allocation into the most aggressive funds that I could as well as my R30K TFSA. I stopped contributing to my RA - as it only gave me 9% last year - and my tax situation has changed.