Nels,
If you are an experienced reloader, I see no problem with a Practical, although when I get my dream 20, it will be a TACTICAL (same brass, longer neck).
If you've already got a 223 and know your way around that cartridge, you're in a good position to move on. That's something I always recommend to friends -- get a 223 first, wring it out, then use that as a jumping-off point for whatever else strikes your fancy.
People rave about the 204...my experiences haven't been that great but that's just me.
It depends on whether you like taking that step into wildcat land -- which honestly isn't that big a deal. If you like getting that last bit of performance out of what will be a custom rifle, then go for it.
