titanium compressor and turbine?????

[rgnissan240sx]

have been doing some research on turbos that would best suit what im trying to build i know i want to hit the 350whp marker but the turbos that can reach that all have more lag than what i desire so i looked into a company that cast titanium parts and they have already done compressors and turbines the result is that they are 33% lighter than steel and will spin at 170,000 rpm but my basic question is does anybody know or can give me an idea of at what rpm would a Garrett GT2871R begin to spool if i swaped out the compressor and the turbine with titanium one any insight would be greatly appreciated thanx