6.5 Grendel is a great caliber but components are more difficult to find. I'm not knocking the caliber but 6.5 Grendel Brass, if you can find it, is going from $0.65 to over a dollar a piece for Lapua where 223 brass is plentiful and a lot cheaper.
The same, to some extent, with bullets. From what I've seen 6mm bullets are less expensive and easier to find than the 6.5's for the Grendel.
The 6x45 is easy to convert from 223. I use a Redding Small Base body die then use a 6mm mandrel to expand the neck. Redding also makes a 6mm/223 Rem die set if you want to go that route.
The one down side is that the 6x45 looks like a 223 so you need to be careful to use the correct ammo. I went to using nickel plated brass for my 6x45's.