I have a .25 Mk2 Crown with the 600mm barrel in a Saber Tactical chassis and I think it is perfect for bench shooting. I have the harmonic tuner installed and it shoots FX heavy pellets and JSB Knock Outs at 910 fps into a ragged hole at 50 yards. It's easy to tune, you just have to put in the time.
My buddy has an Impact M3, also in .25, and we shoot together often. Tuning his M3 was much more complicated and time consuming.
For the money, it's hard to beat the Crown in the Saber Tactical chassis. If you got the Impact M3, you would need to add the buttstock, bag rider, cheek riser and front rail just to get the level of adjustment of the Crown.
On the bench, with an AccuTac F-class bipod and a bag in the back, the Crown is rock solid.