Well, that question is not as easy. Not sure the size of the cap will make that much of a difference. It really depends on the capacitance of the IC your using and the output impedance of the preamp. Yours has an output impedance of 600-1000 ohms depending on the volume and frequency. Impedance will rise as you turn it up.
Best case in an output impedance of under 500 ohms to avoid top end roll off on a long 4-6 meter IC. How long are your ICs and what are they?