I am awaiting the arrival of a pre-loved Mono Speedy 35 to be used as a purse. In the meantime, I am eyeballing a Mono Keepall 45 (no strap) for carry-on. IYP, what is the size difference in terms of amount you can stuff into them? Would it be better for me to use the Speedy 35 as carry-on? FYI I regularly use my Mono Speedy 30 as a purse and it is never full. Thanks for any advice!