I haven't made an animated GIF before but you might try using the bit-rate parameter to specify quality, in spite of it being an image (and presumably having no rate). Thumbnail quality responds to the -b parameter. If by insane, you mean, "insanely bad," you can specify a very high bitrate and bitrate tolerance (not sure if you're using vbr or cbr source). (or do the opposite if you mean it's too good and you want to limit size)
'-b', '10000000','-bt', '20000000'
Alternatively, you could also change the dimensions using the -s parameter, which will take an ordinary looking representation of the dimensions like "1920X1200".
It really depends on the bitrate and compression of your source material and what you hope the gif will be like. Maybe consider providing more info than "insane," but I imagine this will give you a good start either way. Good luck