The advantages of brushless:
-Basically no maintenance: remember skimming your commutator, replacing brushes and springs etc. You don't need to do any of this with brushless (i.e. you can't do any of this with brushless). The only maintenance required is to keep them clean and check the bearings.
-The motors are more efficient which ends up with faster motors that run cooler and consume less power.
-As the motors stay cooler and there is no comm skimming, they have a longer overall lifetime.
NB: The 5.5/6.5T you mention is the 'turn rating' of the brushless motor. They are all slightly different speeds, like brushed (one 27T is quicker than another). 5.5T and 6.5T would be modified, a 10.5T would be the super-stock (19T brushed) and a 13.5T is stock (27T brushed), though they will all be faster than their brushed counterparts.
The advantages of LiPo:
-One pack should get you through a race day, as they will recharge and won't complain like an old NiMH would.
-They are far lighter than a NiMH pack.
-The overall lifetime is higher than a NiMH pack which would lose its 'punch' after about 20-30 cycles, in comparison with 100-200 cycles for the newer LiPos.
-They have a lower internal resistance than NiMH, and have the ability to provide far more current than any NiMH cell. This is what the 'C' rating refers to. A typical NiMH cell has a 10C discharge rating, whilst a good LiPO has at least 30C discharge rating. Therefore it can provide three times the power of an equivalent capacity NiMH cell, meaning cars are again faster.
-They have a higher power-to-weight ratio, even the higher capacity LiPos (like 6000mAh) are far lighter than the highest capacity NiMH cells (around 5000mAh), and are able to provide more power.
PS: I like the CAT SX, though as many have said, check with the club to see what's popular just in case brushless and LiPo prove too much and you hit something very hard, and need some spares.
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