I am knew to the lipo thing and have a couple questions. Example: If I have a 1600mah 30C battery and switch to a 1800-1900 mah 30C, what would the benifits be. Is it just longer run times or is there a noticable power difference. I am getting mixed explanations from my LHS. thanks

More Mah mean more run time, so going from 1600 to 1900 ur gonna gane maybe 5-10 mins depending on how u drive your car, now u can join two packs together is seris to get more pwoer. But if u do this u want the pack to have the same C rating and the same MAH, Hope this helps

With Lipo things can get a bit interesting on this subject.
You will definitely get more runtime with a higher mah, and you may get more power too, depending on your setup and how you drive.
1600mah 30C = 48 Amps
1900mah 30C = 57 Amps
If you are using a small car and high turn motor that never sees 50 amps, then you will not notice a difference in power at all, just more runtime.
BUT if your setup can use more than 50 amps or so then you will gain performance as well as runtime. i use Lipos between 1600 and 2500mah in my mini Rc cars, and I never hit those kinds of amps. But I am also running on a small track that is slick. In my 10th scale I think it hits peaks of 80-100 amps at times.

LiPo ratings are a factor of a couple different numbers.

Capacity is the ratings as stated 2000mAh, 3000mAh, 5000mAh.
"mAh" stands for MilliAmp/Hours, or drop a few zeros & you have Amp/Hours

A 3000mAh or a 3Ah battery can sustain a 3amp load for an hour.
A 5000mAh or a 5Ah battery can sustain a 5amp load for an hour.

The real fun is the "C" rating.
It is a measurement of output based on a Multiplier of the mAh rating of the pack
20c = 20 times
30c = 30 times

3000mAh or 3Ah x 30c = 90amps <--- Some punch
5000mAh or 5Ah x 20c = 100amps
5000mAh or 5Ah x 30c = 150amps
5000mAh or 5Ah x 40c = 200amps <--- Lots of punch

The higher the "C" rating combined with the mAh rating is the "punch" or capable output of the pack.

When you "parallel" up packs of the same type the "C" rating does not change, but the available amperage is doubled by the math...

3000mAh + 3000mAh = 6000mAh x 30c = 180amps

When you "series" packs the voltage increases...

For 1/10th scale 3800-5000mAh 7.4v 20-40c packs are very common.
1/8th scale 4000-6000mAh 14.8-22.2volt 25-40c packs are common.