I would suggest the 3.5 or similar knife even though I don't own a 3.5. I do own a GSO-10, 5.1, & SK-4 (previously a 4.1 as well), and while the 5.1 is more of a stand-alone blade, the 4.1/4 is just a little too big for me to piggy-back. That typed, I regularly carry the GSO-10 and SK-4 around the property and think them an excellent combination. I need to sell one of my GSO's in the near future, and the 5.1 will be the sacrifice as it doesn't get used as often as the other 2. I didn't go in for the 3.5 because I prefer folders in that size/role. That's my $0.02.