Do I need a f2.8 ????

I am switching from a CP8700 to a D70

I shoot Friday Night HS Football Games.

Was shooting full zoom on the cp8700 which is (35mm eq) 280mm
Lens goes from 2.8 to 4.2 so I was probably close to max of 4.2

No flash- ISO set to max 400, then lighted picture with Computer and removed noise using Ninja 2

Now going to be using D70 with SB-800 Flash

As I pay for the whole thing including web site...

What is the least expensive but best lens for the ligh, speed, and distance.

I do have some money to spend, so it's not like I want a $99.00 lens

My D70 (I just ordered it) Comes with the 18-70 DX and the
Nikon 70-300mm f/4-5.6G AF Zoom-Nikkor Lens (not ED)

Please help a novice to SLR's..

Thanks in advance

--
John say's H.S. Football Photography is my hobby.
My wife is my passion