Depends on how deep your pockets are but personally I wouldn't bother pumping money into a turbo that runs out of puff in the top rev range. I have been down the route of hybrid ct9s and they are a good upgrade if you want a little more punch higher up and you don't sacrifice a lot spool time, probably 200-300rpm with a tongs or speed vision hybrid ct9. You could go down the route of a billet wheel to reduce weight and spool but when you can pick up a tfo35 from a subaru forester from around £100 and a good manifold and down pipe combo it really isn't worth it. Or go td04 for more power there cheap enough. A td/vf series turbo at low boost boost will alway be better than a ct9 at max efficiency. Less boost, less heat, less stress. I'm only going on my own my experience and knowledge gained off this and other forums over the years.