Love my 21 910F, but the 17 910F wasn't consistent.  Being LH, there aren't a lot of clubs to try in stores.  By semi-accident picked up a TM Rocketballz 3H (stock 65 g R) and also finally found a 910H 19 Ilama R.  Still using mats waiting for spring, but put them side by side. 

Wasn't even close.  If I had taken the TM challenge, I'd owe them over a half-dozen balls. 

And only one had the snap/crack sound letting you know you got the sweet spot.