The new Audi SQ7 TDI does what you were going trying to accomplish. They utilize a 48 volt system to spin up the turbocharger. You may want to check it out, pretty interesting stuff.
The 3 diesel generators I've worked with/on, two were 10000 hp enterprise/delavals which ran at 450 rpm and were rated for 7.7 MW and an EMD two stroke tandem arrangement which ran at 900 rpm and was rated for 3.3 MW