I hear that, but I have a little less trust in Calman. They screwed me over on what was the C5 (Chroma 5 pro). The thing was never accurate, as proven with a reference meter yet they said it was. Also, are you just looking at the D3 (non pro), or i1display? Tom's version uses tables, just like the C6, based off a reference meter. If you were gonna go Calman, ideally its a I1 Pro 2 and i1display, and then profile the i1 at the time of use.
I can get Tom at all times, even on the weekends via email, and the D3 Pro so far has done a great job.
If I had to pick one right now, I'd use CP and a D3 Pro, but of course you have to use ControlCal. I used the Calman 5 software a good bit last month, and while it is much better to me than 4, I still like Chromapure. I've found the D3 Pro to be fast, and now they tweaked the low light handling it's even better. It wasnt that it had accuracy problems before, its just every now and then you'd get some funky reads at 10% on plasmas, at least dark plasmas. So you had to take several and kinda see the consistency.
With the latest beta I took almost 20 readings at 10%, spread out among gamma and color runs, and they were mostly consistent. Also, just looking at the meter's level of accuracy, you are splitting hairs with a D3 Pro vs a C6. I can get the VT50 at less than 1 deltaE on several grayscale points, but then whats the inherent error of a cheaper meter
Long story short, i think either a C6 or D3 Pro is a fine choice, i just prefer the CP software and Tom's support. Calman acts like a bigger company at times, whch they are, but I like quick customer service too.