44,100 samples per second, 16 bits per sample, and 2 channels. 44,100*16*2 = 1,411,200. That's in bits, so divide by 8. 176,400 bytes per second. You said 4 minute song, so multiply by 240 seconds. 42,336,000 KB, or ~42MB.
And no, you won't get better quality recording from the line-in. There's still issues where you could get a transmission error. And plus, recording would be real-time, i.e. 1x. USB 2.0 runs at a theoretical 480Mbps. Much faster.