Peep this.
http://www.miata.net/garage/tirecalc.html
Assuming your stock tire size is 175/70/R13, you would want to go with 205/35/17's and your spedometer would be spot on.
Personally I wouldnt want my profiles that thin, and I dont even think they make those, so I would probably go with 195/40/R17's and have my speedo be 2.2% too slow so if the speedo said 60 I would really be going 61.3mph