Having a look at their site now. Could you possibly link to one that would pass as carry on?
These are fine:
Talon 44, Atmos 35.
Slightly over BA allowance but not by anything significant so you'd be fine I reckon:
Porter 65, Farpoint 55, Hornet 46.
But remember, it's not the size of the bag - it's what is in it.
Though, when I replied I was speaking generally and not saying that it is always possible and it's often less advisable as lightweight travelling really is a skill.
You're a new traveller, and travelling light weight brings issues which carry a lot doesn't. Namely, you've got to find places to clean your clothes, not able to bring anything back. But there are many pluses also.
If I were you, I'd take a medium size (perhaps the Aether 60) in the hold, as that way you have the safety net that is probably advisable for a new traveller.
I just don't want you to get over there, and realize that your bag is far to small for your needs because I said that it's possible.
Work out where you're going/what you want to do and then you can work out what you'll need. If you're only going to be in cities then you aren't going to have to pack hiking boots, roll mats, appropriate hiking trousers and such. If you're going to spend most of your time in the countryside then you won't need smart shoes, suit trousers, and things like that. If you're going to be at beaches a lot, then you'll need even less. Once you've got that sussed you'd be in a better place to determine what you'll need to take. Bear in mind though, that you can buy a lot over there and it'll be cheaper than getting it over here.
Travelling light is far better, I'll never understand travellers who walk about with a 120l rucksack on their backs and a daysack on their front struggling to keep up and sweating madly, but it is a skill and not for everyone I guess.