I've been using a stock Gen 3 Glock 34 for IDPA, USPSA, and 3Gun for several years now and have around 30k rounds on it. I'm thinking of finally dipping my toe into optics and getting a pre-milled aftermarket G34 slide. Is there any reason to not just use the same barrel or should I spring for a new one?

Also, any suggestions on reasonably-priced sides? I've been checking out the Brownells offerings, but they seem to get mixed reviews.