It's pretty negligible. I genuinely can't tell the difference between NTFS and ext3 at least performance-wise.
However, the locking semantics on NTFS are shitty unless you know what you are doing (i.e. use KTM/Transactional NTFS) which sometimes skews the statistics a lot.
Say you had a "write/update infrequently, read many times" system profile with 10% disk space avail. It seems like Windows would store these files closer to each other on the drive, making reads more efficient.
Or would that be such a negligible difference that it's not worth mentioning?