Smaller battery for a GSX-R 1000

I am looking for a smaller battery for my 06 GSX-R 1000. Does anybody know how small of a battery I can get away with on the bike without taxing the electrical system and still being able to start the bike everytime?

Here are the specs of the OEM battery if that can help in anyway.
Battery Family: Maintenance Free
Battery Type: YT12A-BS

Voltage: 12
Capacity (Amp. Hrs.): 9.5
Dimensions: 6" x 3.4375" x 4.1875"
Weight: 6.3 lbs.
Metric Dimensions: 150mm x 87mm x 105mm
Metric Weight: 2.8 kg
Polarity:
Acid Volume: 0.5
Charging Current (Amps.): 1
C.C.A.: 175

 

Yeah someone sells a battery for about $200 that's super small. I forget the name of them though. I think thye have 2 different kinds

 

Speed Cell .. superbike model is what your after.

 

Those speed cell batteries are pretty impressive, they only weigh 1.7 lbs. The $250 price tag is a little much for my vintage bike.

Do you guys have another other suggestions of smaller batteries that could work?