Id stay away from SBR turbo's. I bought one and overall its just not what it should be. I live about 2 hrs. away from bullseye turbos and I would buy there turbo next time. I learned so much for those couple of hours that I was up there, it just amazed me.
As for your next turbo, if your not even pushing your EvoIII to its limits yet, then like someone said above, a nice 50 trim would be an excellent choice. Still has great spool up, around 3600 for full spool for me, and has great top end, doesn't fall off up top like an EIII would. Even w/ a proper internal gated setup, you should have no problem w/ creep issues.
Heres bullseyes website. I would definetely rate their customer service A++, They gave me a new turbine housing, instead of just fixing it or denying it. So I rate them great products w/ great service.
www.bullseye-power.com