Iv recently replaced my rads as mine were a bit grotty and i was seeing quite high temps in traffic.
What 'sort of' temperature should i be seeing when the fan kicks in?
At the moment mine comes on around the high mid point of the temp gauge though the temp quickly drops to 90ish when it does come on.

Is that right?
surely if the gauge is linear then the temp must be nearly 130 before the fan comes on!

You could try the service manual in he document library on this website.

Stock fan switch, located on the left side of the lower rad, has "100 ON" engraved on it.

So it's 100 degrees Celsius give or take a few.