A mid engine car is not faster than front or rear engine car. On a production car basis, with a gas-burning engine, the quickest car around the N-ring is/was a front engine Japanese made Nissan.
However.... a car with the engine in the middle in mortal hands, is the platform that is the easiest to drive fast. A car without a roof, designed to be a roadster (and not a car with the roof hacked off afterwards like the Carrera Cab) avoids increasing the center of gravity, which in turn makes the car more of a "point and shoot" experience. The only Porsche, with a conventional engine, that has both of these things is the Boxster. You can add a fixed roof for rigidity, like in a Cayman, but the extra weight up top will cost you on handling. You can make the car longer and wider like the Carrera, but it will also cost you on handling.... partly why the 991 GT3 now comes with RWS, to give more of the short wheel base feel of a Boxster/Cayman and avoid that abrupt weirdness of (pre-991 GT3) bigger Carreras. You can add AWD like the Carrera C4 but the inevitable understeer (the way Porsche do AWD) will cost you on handling. So with the Boxster you get RWD, Mid-engine and lower COG.
(for color, see the huge gap on the time sheets below considering the tight track conditions)
http://www.excellence-mag.com/issues/196/articles/open-and-shut-case-track-test
As far as power, if you can swing a 2009 Boxster, it's the best option because unless that 2000-2002 has low miles or the seller did a bunch of work that he's not expecting to get back on his asking price, you must budget in some big repairs if mileage is over the ~60K mark. Having a few back to back repairs, that didn't rear their heads during the pre-purchase inspection, that equal 30% of the purchase price is not unheard of. In other words, there's no such thing as cheap 12 year old Porsche. Over the first 60K miles of my Boxster S experience I had exactly one unexpected repair that ran over $200. After 60K miles... it was payback time in a big way.