(That )S(that ):S(is )::SS~::SS~:(not )*:SS:S~S(it ):SSS
(that's 128) are rather repetitive, so a more efficient way to build large ones is by applying other numerals to each other.
That's 2^2^2^2^2 or 2^65536. Then you might try to compress the :'s and ^'s similarly, although I don't think that will help when there's this little room to work within.
Thanks! One of my original approaches was something similar to this, (
()(^)(:)(~:*:*~):^:^:^!^^) but it took less cycles than my first approach. (This took 160 cycles, my first program took 532)