I had two of the case hardened Gauchos in .357, with 4 inch barrels. These were good guns and very accurate. I gave up the cowboy stuff and sold them both. There are some places where you can buy custom grips for the guns, and I highly recommend it.
I liked shooting the .38 ammo out of the guns, since it was cheaper and I don't reload. However, many cowboy folks prefer the .45 LC since it is slightly more "authentic" and also it just feels really good to shoot the larger bore.
The choice is really yours. Do you want to be cheaper and more competetive (.38) or more authentic (.45 LC)?
got a 357 gaucho in ss with the 5.5". Shoot 38's through it.
What kinda/caliber of rifle do ya have?
I matched my pistolas caliber with my rifle. The other pistols I have are Uberti's/Cimarron's,now these are very nice and to a degree expensive. But Uberti has more models (ie. 1873,1851,1860,1847) that are useable for cowboy shoots.
If you're serious about the competition and plan a lot of practice and don't reload, you better stay away from .45 Colt. EXPENSIVE! I have one, but I handload. I'd sure go with the .45 if you handload. It's much easier to make accurate with cast bullets, though .38 wadcutters can be tack drivers with about 2.7 grains of bullseye driving 'em. ;D