Here are my .22 J-frame rimfires, top down, a 5" 63 (.22 LR - recent), 4" 651 (.22 WMR - 1999-2000), and a 3" 63 (.22 LR - current):
The 651 was bought a year ago, ANIB, for $550 locally. It was a Holy Grail gun to me. My 3" 63 was bought two years ago - and is a keeper - it was more. The 5" 63 was bought from a friend's estate 9/2009, following my first rimfire revolver - a 4" 617 a year earlier. It is a hard act to follow - but it's a K-frame.
Back to the 651. If I didn't have it, would I consider rechambering an existing 63 in .22 WMR? No way! All you gain is enough fps to make it's rounds supersonic - and produce a loud 'crack' instead of a 'bang'... and a far greater drain on your wallet, too. Besides, I believe, someone correct me if I am wrong, that the barrel will need to be slightly reamed, as .22 WMR is slightly larger in OD. IF the OP's interest is not reamed, pressures may be higher - and leading/copper deposits may increase, too. I'd avoid that choice.
In use plinking, the 3" 63 'tickles' some rebounding steel plates, while the 4" 651 will drop them. But - so will my 5" 63 as it gets a few more fps from the LR rounds. CCI Stingers in .22 LR from my 3" 63 are nearly as impressive at 12yd blowing up a pop bottle full of water as the 4" 651 is with Hornady Critical Defense ammo. One .22 WMR J-frame revolver I would consider - and so does the well-respected Mas Ayoob - is the 351C/PD. The 10+ oz Airweight will set you back $600+, however. Is it equivalent to a .38? Not exactly.... if that is what you want, just get a 642 or 442 - $400 or less. Typical defense ammo recoils too much? Try 148gr LWC target ammo - almost four times the mass and makes a larger entry hole than the expanded rimfire would - at a minor recoil.
Stainz
PS In a horrid future, where I could only keep one of the above trio - it would be the 3" 63.