Those temps are still just fine for non-synthetic 80w-90.
The friction additive that you reference is not the same as the friction modifier that I am talking about. The one you reference is an antiwear additive for gears, with lots of moly in it. I imagine it is similar to the Dow Corning Molykote M.
The friction modifier I am talking about is specifically made to keep multiplate clutches happy; Here is an example:
ford racing friction modifier
I don't believe that pelican sells this type of product but it is available at lots of local auto parts stores, it is not hard to find. the Red Line tech told me it doesn't matter much which brand you use, but not to exceed 1/2% in a 901 or 915.
You _only_ need to add this if you have a multiplate clutch limited slip like the factory one and exprience limited slip chatter, which usually manifests itself as a slight vibration at low speed, for example pulling away from a stop sign and turning fairly tight. this chatter doesn't really hurt anything but can be a nuisance. If you don't have a limited slip there should be no reason to add any friction modifier.
It would be good to check first if you have a limited slip, but if you do have one or can't check, I would start with Red Line 75w-90ns or the Delo I mentioned above and add friction modifier only if you find out you have a limited slip and experience chatter.
With your temperatures the Delo should be just fine, and it is a very high quality non-synthetic oil that would cost less than the Red Line. Both are very good, though.
The lubro moly may be very good as well but your local mechanic is the first person I've heard of using it, so it's hard to say. I can't conclude that the product is made without friction modifier added without more information, which I believe is the key thing for porsche synchronizers in synthetic oil.