in regard to being too slippery and the synchros not grabbing correctly causing gear rake on upshift.
Yes, I had that problem with my previous car (1998 Subaru Legacy GT).
The owners manual said to use 90W gear oil in the manual transmission.
So I put some 90W Castrol synthetic gear oil in hopes to improve winter shifting. Over a matter of weeks the shifting became more difficult because the syncros were slippping too much. I replace it with cheap Castrol 90W gear oil and the shifting improved.
I later read that manual transmissions require some friction additives so that the synchos will work properly. I bought 4 Liters of Red Line MT90 for my Subaru but sold the car before I put the stuff into it.
Red Line MT90 is a synthetic manual transmission oil specifically made with special friction additives to improve shifting performance and reduce wear in manual transmissions compared to much cheaper OEM fluids.
http://www.redlineoil.com/redlineoil/mtlti.htm
You are right the MT90 is too thick for Honda transmissions.
Red Line MTL is a much better choice.
I'll try to sell my MT90 and buy some MTL instead.
I'll let you know how it feels in a few months (it's too cold for me to physically change it anytime soon).