Hey, sooner or later i will be upgrading my amp to a Hifonics amp 1206D or 1606D.

1206D
RMS @ 4-Ohm: 1 x 450-Watt
RMS @ 2-Ohm: 1 x 900-Watt
RMS @ 1-Ohm: 1 x 1200-Watt
Hifonics New Illuminated Heat-Sink Design With Blue LED Light Pumps
Hifonics Blue Illuminated Logo
Maxxsonics Illuminated "M" End Panel Logo
Heavy-Duty Ultra-Fi™ MOSFETS
Highly Efficient Super D-Class Amplifier Circuitry With Oversized MOSFET Output
Fully Adjustable Accu-Cross™ Crossovers
±18dB Variable Bass Equalization @ 45Hz
180° Variable Phase Control (15 to 35Hz)
Dash-Mountable Bass Remote Control Included
Variable 24dB Subsonic Filter
Brutus Pulse Wave Modulated MOSFET EXVP (Exponential Vari-Power Supply)
Twin-Turbo Torroid Coil Design
HSMD Hifonics Surface Mount Design
Balance Line Inputs for our 18-Volt Line Drivers
RCA Line Output for Amplifier Daisy Chaining
Gold Oversized 2-Gauge Power Connectors
Power From The Gods Included

1606D
RMS @ 4-Ohm: 1 x 550-Watt
RMS @ 2-Ohm: 1 x 1100-Watt
RMS @ 1-Ohm: 1 x 1600-Watt
Hifonics New Illuminated Heat-Sink Design With Blue LED Light Pumps
Hifonics Blue Illuminated Logo
Maxxsonics Illuminated "M" End Panel Logo
Heavy-Duty Ultra-Fi™ MOSFETS
Highly Efficient Super D-Class Amplifier Circuitry With Oversized MOSFET Output
Fully Adjustable Accu-Cross™ Crossovers
±18dB Variable Bass Equalization @ 45Hz
180° Variable Phase Control (15 to 35Hz)
Dash-Mountable Bass Remote Control Included
Variable 24dB Subsonic Filter
Brutus Pulse Wave Modulated MOSFET EXVP (Exponential Vari-Power Supply)
Twin-Turbo Torroid Coil Design
HSMD Hifonics Surface Mount Design
Balance Line Inputs for our 18-Volt Line Drivers
RCA Line Output for Amplifier Daisy Chaining
Gold Oversized 2-Gauge Power Connectors
Power From The Gods Included

I know im going to need a cap but i dont know much about how much farads will be needed. Your recommendations will be my guide when I go to buy.

And also i have 4gauge only and both these amps take 2gauge what are the cons of this and should i upgrade to 2 gauge also?

You will be MUCH better buying some wire and doing the big 3. If you really wanna spend some money, go but a better battery to match that big 3.

As for the wire, you might get away with 4 gauge, but I recommend bigger.

__________________
RD Audio =|= Sundown Audio =|= Elevation Audio =|= UltraLinear

I'd stay away from caps .. they put more strain on your electrical system.
http://forum.realmofexcursion.com/showthread.php?t=17970
that page will explain everything.

but wouldnt the amp suck my battery dry quickly?doesnt a cap help?

No it won't help.