I'm not a comp shooter, but personally, I find that for marksmanship, the longer the better, pic related is my striker fired long barrel.
Even for CC, it doesn't matter so long as its under, eh 4.5 inches? For 6 oclock, my biggest concern is just not having it be long enough that it interferes with sitting (sitting on the barrel or pistol rises up because barrel is supported by seat). But I digress.
Guns arent terribly expensive and you're probably going to spend about $600 or so maybe for a gun, and it'll maintain its resell value fairly well (especially if you buy used). If you stick to buying used, you may end up actually not paying more than a new standard size, and I don't think it would necessarily hurt to have a small collection of different guns, even if you didn't fall in love with the first one, it might still not suck for trying different sights or just something different every once in a while.
Plus, longslides are sexy. My vote is go for it.