FWIW I tried it and it was fine.  I also loaded the 757-200 full both pax and cargo, and by using the count-the-tick method arrived at a CG of 40% and up trim of 2.5, which seemed to work better than the greater trim I had been getting with the default 27%.

Heavy cloud cover with REX, and I'm chugging a bit in cruise sometimes with frames.  Of course unlimited, infinite clouds are a nice setting for the 757 and with automated flight I'm not having any problems (except for heavy turbulence).