I made the switch and with a top rated 54" Panasonic V10, I can't really tell much difference.
This is not a side by side, but just a casual observation.
Others may argue otherwise.
A couple of things though, I get way less audio dropouts with TSTV and the PVR features leave SD in the dust.
Both reasons I left SD and Shaw cable after many many years.
The other upside is the TSTV firmware did NOT get updated like Bell did and thus is not suffering the rash of problems they (Bell) are having.
You ultimately have to look at what factors are having you kick the tires of the competition.
While SD typically has great customer service, the fact that you may be dealing with Telus and not Bell almost makes for the best of both worlds.
A decent PQ, AND CS all in one with a fabulous PVR.
If the comparison where SD vs Bell, I'd say stay with SD though.
You can always try a TSTV rental for a few months to see for yourself.
With SD, you are buying into the whole system, but since you are an existing sub, this is not an issue, but would be for someone making an initial decision.
While it's entirely possible the new SD gear may be fantastic and we hope it is, you are dealing with a new unproven 6XX version 1.0 while the others guys have a long legacy of products that are supported by a genuine going concern.
I just wish I could say that about both SD and Motorola given what's been happening.
So an unseen, untested unit or a mature unit with features SD can only dream about.
We all know the promise of the 530 never materialized after 5+ years to 'get it right'.
Has anything really changed over there to think otherwise?
Good luck with your decision.