From what I can work out, the spatial extensions are very immature - sort of like Oracle Spatial 1 (8i) compared to Oracle Spatial 2 (9i).

Where I used to work had to make a choice between OS1 and going with Oracle normal. In the end we went with Oracle normal and doing the spatial calculations with stored procedures instead.

I've been out of the company now for over a year so I don't know if they have switched across to the latest Spatial (was it updated for 10?) but with 7.5TB of data I would doubt it very much.

Which leads me to something else - no one has mentioned that doing a 50km "circle" for searches won't produce an exact circle, more of an egg shape, but since you are interested in precision (we used to work to centimetre precision) a couple of hundred metres here and there won't make much difference.

G.