69 mm/rev is a bit low for 20deg timing. I'd be around 73/75 with that timing. If you don't have enough timing or enough load on a motor it can get as hot as if you too much timing and/or gearing.
Not used a TP before, but checking on the Schumacher website Chris Ashton was running one on 38deg timing at 69 mm/rev in a SupaStox. I'd try upping the timing in the same gearing and see what that gives you.
Yes the LiPo makes a difference. I have one that is excellent and one that isn't. The poor one is 0.2s a lap slower. Both are nearly new and raced only ten times, but still one is not as good as the other - replacements due!
However, don't assume that getting a new LiPo means you get a faster LiPo. Stick with what you have, get the most speed you can from the current equipment and then see if someone will loan you what they think is their best LiPo for a race. If you can't feel a difference to your Orions, keep the wallet closed!
If you are talking top end, then the speedo is not likely to be the culprit. Same thing applies - get to drive someone else's car with your LiPo in and see what that feels like.
Too much credence is given to assuming that if the car is "too slow" or "being passed by everyone else" then it must be something in the motor/cell/speedo when in fact it could simply be better driving or better set-up. Keep trying before you keep spending!
