Aside from the cost, ($80.00 each), Titanium valves will not survive the extreme exhaust temps that turbo engines (tuned on the edge) will generate. I find that my EGT's run 1550 to 1600 degrees when my engine is running good.
Check out the Manley web site. They are one of the biggest titanium valve suppliers. They will tell you that the yield temp of titanium is well below the temps I quoted above.
Titanium valves are typically required on engines to reduce valvetrain weight with wild lift cams. Our turbo engines do not need wild lift or duration cams to produce BIG power.
I think lazy valve lift and timing are one of the biggest advantages our engines have. We don't need big buck valve springs, roller rockers, roller lifters, titanium, retainers, valves etc. Roller Cams are nice but not needed IMO.
Save your money and buy Stainless Steel. Lots of Options, alot less money.
Just my $.02
Dave Roland