Well in answer to my own question....
100 amp relay was fine running off the sidelight.
I would have got a 60 or 70 amp relay but they use a stupid spade connetor which it is only possible to get the spade connectors with a maximum cable diameter or 6.something mm. This is a problem since the 70 amp cabling is 8mm thick.
So I was forced to go for a higher powered relay to support ring terminal connections instead of spade connectors.
This meant a minimum of 100 amps. Annoying eh???
Still im happy with the install and the HUGE relay which was housed neatly where the ABS should be.
vehicle wiring products (google it) did a fine job of sorting all the kit I need for slightly less than the centech relay cost plus I can safely say that my wiring wont fry at full capacity which I cant honestly say that about the OE curcuit.