1) Center drills are about 3X as stiff as a spotting drill because less material is removed for the flutes.
2) Here in the U.S. the "cost equation" for center drills versus spotting drills is reversed. A good quality spotting drill costs slightly more than double the cost of a good quality center drill.
I am with John here ,,,,,,,,,, spot drills are stiffer ,,,,,,,,,,,,,,,allot stiffer
Yes they may be a tad more expensive,,,,,,,,,,,but they can be re-sharpened
,, ever tried re-sharpening a centre drill ?
Rob