Yes more current available. Longer run times. With more current availalbe you have more acceleration. Say you have a 3s 20C 3ah pack. At most you can draw 60A. Now put two packs in parallel. The voltage stays the same but now think of it as one 3s 20C 6ah pack. Now your current draw capability doubles to 120A. So you havbe more juice availalbe when you need it. But you need to be careful. Make sure your ESC can handle that current draw. When you hook packs in parallel the AH adds. When you put the in serial the voltages add.
It's not quite as simple as all that. If the two packs are rated the same, such as...
2s2p 5000mAh 20c
2s1p 5000mAh 20c
You will not have a higher current rating from the 2s2p pack. The 2s2p pack will be composed of 4 2500mAh cells, while the 2s1p pack will be composed of 2 5000mAh cells. However, both packs should perform very nearly the same, taking into account difference in cell quality and manufacturing.
In short, there is no way for us to answer your question without knowing what packs you are asking about ;).
It's not quite as simple as all that. If the two packs are rated the same, such as...
2s2p 5000mAh 20c
2s1p 5000mAh 20c
You will not have a higher current rating from the 2s2p pack. The 2s2p pack will be composed of 4 2500mAh cells, while the 2s1p pack will be composed of 2 5000mAh cells.
I would also add that you have twice the likelihood of a cell failure in a 2P pack versus a 1P pack.
“Everyone has a right to be stupid; some people just abuse the privilege.”
What is the maximum discharge rate? The big C value that is on the pack. You might not need more mah. Depends on the weight of the vehicle and gearing and what not. Best way to learn is trial and error. Use one pack for now, then either increase pack capacity or put two in parallel. So you could buy two packs, and use them seperately. As soon as one pack dies switch out and put in the other. Probably give you more run time than putting two same paacks in parallel. This is only because you are pulling around the weight of one pack at all times. Now if you need to draw more current which is unlikely then you will either put them in parallel or go to a bigger pack with a higher discharge rate, if not already there.
The pack you're looking at is 5000mAh and 25c. 5000*25=125,000. 125,000mA is 125 amps. So you are looking at a pack with 125A continuous discharge, ADVERTISED. Unfortunately we can't really look at the manufacturers ratings as 100% accurate.
TP's are nice and all, but you might look at some trakpower, neu energy, polyquest. There are a few others in that price range that might do a bit better than the thunderpower, although TP makes some excellent packs too.