the thumb has some neck-dive. those who can handle the thumb will deny that.
well, the streamer doesn't have neck dive.
it's sits in a comfortable 40° angle.
my 4-string streamer weights 4.6kg. (don't know how much your thumb is)
also, i heard that the thumb feels quite odd at the beginning because the first fret seems out of reach.
the streamer doesn't have that problem.
now, in my humble opinion, the streamer shape is the perfect, because it balances well, the body is not too big, but large enough so it doesn't have neck dive or look silly on a tall guy.
now, in case you wonder how the streamer sounds compared to the thumb:
in my opinion, the growl of the thumb is more like snarling, while the growl of the SSII is more like rumbling thunder.
it has more and deeper lows, and a good dose of low mids. the mid frequency of the thumb seems to be a bit higher, am i right ?
when you look at the pickup position, you will understand why