Sounds like you already bought them but are second guessing yourself. Why? I think you did great. You already had the flagship Diamond 10.7's so the proper center would be the 10CM. And while some may consider the 10.5's (a tower) as overkill or rear surrounds, they will more than work and save the cost of stands if you had gone to a monitor type. So I say bravo!
I once had a full 5.0 set of Diamond 9's anchored by the top of the range 9.6 and really enjoyed them so I am very well familar with their capabilities. Best of luck and have fun listening to them.
Marantz PM15S2 LE, Oppo BDP-103, Simaudio Moon 100D DAC
VPI Traveler V2 with an Ortofon Rondo Blue and Simaudio Moon 110LP, Technics SL-1400 with an Audio Technica AT-14sa and Pro-ject Phono Box S
Dynaudio Focus 260's, Rel T-1 and a Panasonic TC-P54S1.