I guess that would depend on how steady your hands are. A TS55 or any other good circular saw will plow through 3/4" base or mdf base pretty fast and easy with a good blade.
Mark your cut line; hold or clamp a speed square at the proper point; set the saw at 45; run the saw along the edge of the speed square and make your cut. The quality of the cut will depend on how steady your hand is and whether you have the piece laying on top of a bucket or something more stable.
It's a bit more cumbersome if you are making a lot of cuts with a circular saw but getting good looking mitres isn't about cutting everything at 45. Cut two 12"-18" pieces of base with an exact 45 inside and outside miter on each end; then use those pieces to check your wall corners; adjust the saw plus/minor a degree or so as you do each corner based on what your template shows you for that corner. One of the biggest mistakes homeowners or DIY make is setting and leaving the saw at 45. By the time the taper is done, there aren't many 45 corners.