Where a wing will stall first depends not only on the airfoils but the taper, twist and sweep. The sweep is determined by the 25% chord line rather than the leading or trailing edges. In this case the 25% chord line's sweep forward tends to cause the root to stall before the tip. The taper in the planform has the opposite effect. These effects cancel each other with the possibility that there may be a residual tip stall tendency. How much of a tip stall tendency there is remaining depends on the amount of sweep forward and taper ratio involved.

Tip stall margin and crisp snap rolls are conflicting objectives. You should deside where you want the compromise to fall between these conflicting objectives before you try to increase the tip stall margin by thinning the tip airfoil.

Thickness is not the only thing that controls the relative stalling angle of attack of various symmetrical airfoils. The generality that thinner symmetrical airfoils stall at higher angles of attack than thicker symmetrical airfoils is not true in all cases.

Because the stalling angle of attack of the S8035 and the unspecified tip airfoil have not been measured in the wind tunnel (to my knowledge) the only other tool to find the answers is a program like X-Foil which is available as a free down load for windows from the Charles River R/C web site. With this program of Mark Drela's you can calculate the polars of the specific candidate airfoils for the reynolds number ranges in question and see what the differences are in the stall angles of attack. Be warned that this is not a trivial effort but it will give you valid comparative results.