dunno about your speedo, its only out a few k's so i wouldnt worry.
One thing people dont think about, is with new tyres, the speedo will be 1-2 k out.
Wear the tyres down about 1/2 way, and its going to affect the speedo around another km/h.
Same when changing from 15" to 16", theres about 4km/h difference.
On the other subject, how long have you had the xenon globes in your car?
Have they started to make the polycarbonate lenses go yellow?
All EF/EL had that problem, that if you put higher power globes in, the heat generated from the globe would burn the lenses, causing them to go milky / yellow.
Just wondering whether the xenons get as hot.