Well, if you get a Chronobarrel, you'll be able to tell the exact fps of the Centurion, but based on my experience with it I would say it's fairly low. The Chronobarrel measures fps of the gun it's being used on and is an ammunition counter, so if that combination appeals to you then you should get it.

Actually, you can't use a chronobarrel with a Centurion because the crb was desinged for elite darts and it won't take Megas.

So you will need to buy a chronograph.

I got ya covered Wafflzz.  Question 1: What is the FPS of the Centurion ?  Well, a stock Centurion with stock ammo reads a high of 72 and an average of 60 on my chrono.  But remember, Megas have a lot more mass, therefore deal with air resistance better, and therefore generally have much greater range approaching 100 feet. (Actual results may, um vary *cough*)

Question 2: Is the ChronoBarrel good ?  Yes it is.  It's not a precision instrument, but the FPS readings are within 8% of my XCoreTech MK3 - interestingly, always lower.  But as Thiefy mentioned, it only works on blasters that have a barrel attachment point. Blasters like the Centurion don't. But Stryfes, LongShots, and Moduluseses [sic] are perfect for this.