Re: Ruger 22/45 vs SR22
I think you answered your own question. The 22/45 has a 1911 grip style, and can even take some aftermarket 1911 grip panels.
You can also get it with a threaded barrel from the factory, and like you said, it's a proven design that's been around for years, and is very accurate.
IMO, the only reason to get the SR22 over the 22/45 would be if you really, really can't stand the field strip procedure for the 22/45, or just want a gun with a slide that more closely mimics the larger caliber semi-autos.
I have a 22/45 with a non-threaded bull barrel, and I love it.