Enroute Controller described a loss of separation event; the reporter noting that had his/her initial plan and/or altitude been used no error would have occurred.

Narrative

A C550 departure was requesting FL380 came from the previous Center climbing to FL340. A CRJ arrival was descended to FL330 on contact for traffic. I called the neighboring Sector and stopped the C550 at FL320 for the CRJ. Approximately 2 minutes later the C550 was level at FL320 doing 255 KTS indicated. The CRJ was doing 462 KTS indicated. I ran out the vector lines and there appeared to be 7 miles between both aircraft. I put a HALO on the C550 and I decided to climb the C550 to FL340 and descend the CRJ to FL300. After the climb clearance was issued I observed the aircraft merging faster than expected; I issued the C550 a 15 degree left turn and reaching FL340 cleared back to original course. Recommendation; I should have either stuck with my initial decision to let the two aircraft pass over each other or made an effort to swap the aircraft out two minutes prior instead of waiting until they were as close as they were. I also should have turned the CRJ and expedited him down; when I realized there was going to be a loss of separation.