The camshaft in the more efficient Metro XFi was different from the garden variety Metros in that it had lower lift & less duration. That favours low RPM efficiency at the expense of high RPM performance -- the torque curve is shifted lower, and peak horsepower is reduced.
I'm no cam expert, but based on those facts, if you can get a cam with lower lift & duration, I'd bet it would help.
FYI: I put an XFi cam into my non-XFi engine:
http://www.metrompg.com/posts/xfi-cam-swap.htm
I noticed a marked difference in low-RPM driveability. The car became much happier to upshift and cruise at lower RPM. I didn't attempt to A-B test it, though.