when i was choosing, i talked to a few Redline reps. though there info is likely a little biased, number of products and applications arent.
Redline offers many many oils, whereas some companies offer 'one size fits all' fluids. Tech's at Redline said D4 was 'more correct' than any of their other products. considering they offer several products that could be used, that means something to me (im not using a product that fits EVERY manufacturer's requirements).....
though i have not searched other products much, i dont think one would find many companies that offer more products. i would think that D4 is better suited than something from one of the companies that only offers one synthetic ATF for ALL slushboxes. that was my point. this is not to say that D4 is the best out there, but im addressing your question/remark.
i have not come across any ATF's that were specifically created to be used in manual trannies, though there may be some. if you know of one, please let us know (that was a point of yours, if i read your response correctly).
one caveat for me: my eclipse requires 90 wt GL4 (GL5 allows synchros to corrode). many eclipse folks love Synchromesh, Synchroshift, and/or a mix of MTL/MT90. the former two are "one product fits all" - while im sure they are thinner than organic 90 weight, they are still being used in two applications with very differing product requirements (ATF vs 90 wt gear oil). that is exactly what i mean (and i think what 87 GT stang was getting at too).
BTW, there are a few folks whom run 10-30 in their WC T5's.
and as always, re-read my first line; this is all just my opinion and thinking.
good luck.