Straps are cheap and not as messy as chaulk, so I vote for them (Haven't used chaulk much so I can't really help). They won't help with grip, but like IW said, use the straps once your grip is gone. In the example you gave, I would've gone strapless
up to the 515 and then used the straps for the 535.
IME its best to use the straps when you feel your grip is going, but before its gone.