Yeh it takes ages to heat up, the rx we have takes like 5 mines of driving to get to running temp but the wrx takes like 10 15 sometimes and it fluctuates from mid way to under 1/4.
I'm pretty sure its thermostat but we had the car booked into Tenagah for a new motor on Wednesday anyway, providing it is thermostat we will be stoked and be able to spend the money on some other bits and peices.

I'll check out the hose to the throttlebody aswell.