Zion is slower than Milaana, at least in my experience. But this more gentle aspect is what allows such an incredible vapor quality and preserving the taste so long into the session. Hmmmm that goodness, just talking about it makes me want to have a bowl but I'm not at home...
Yes it's best to use a matched pair, but it's not the end of the world either if you don't. Use your HG2 cells but watch the voltages closely at first. If you end up with a wide difference in resting voltage at the end it can be problematic. For instance if you end up with one at 3.2V and one at 3.4V when they both started at the same voltage, it's a sign they would not make a good pair.
Pairing is nice but even when doing that, cells can age differently and minute differences in their internals can make them drift apart. So I would advise anyone to check their resting voltages from time to time to see if there's a large unbalance. Even working pairs can take different routes and need to be separated.
Ideally you would want to pair them by IR (internal resistance) regardless of their age. Don't see these pairings as static, that's the mistake. It's all dynamic.
I expect my production Zion to be one of the last delivered. If I like it as much as I like by beta I will be very happy. If I like it more than my beta, well, Mechanophilia could become a concern... 
