We can also help compare.
I'd try turning him around again. It's FAR FAR FAR safer, to the point where I'm just not comfortable recommending a forward facing seat at all (and in fact, one I would recommend is not allowed because the company realizes he should be rear facing). The children here generally rear face to three to four years old. We get through the stage where they push on the back (nearly all kids do, they hate being restrained. He'll probably fight you again, in either direction, around his second birthday), we get through the stage where their legs are bent or straight or appear to be uncomfortable. And they can straighten their legs. Easily and more comfortably rear facing than they can forward. Forward facing they have nowhere to rest their legs. They get dangling legs, which can lead to bum and back numbness or pain.
See, straight legs. The Marathon doesn't offer a lot of rear facing leg room or forward facing leg support, so if he's all legs he'll likely find it uncomfortable in either direction after a time.
Also, his legs are safer rear facing than they are forward. The video at the bottom of this page, "Rear facing vs forward facing position in the car," explains it very well.
http://carseatblog.com/5168/why-rear-facing-is-better-your-rf-link-guide/
Seats that offer a lot of leg room and can help him meet the AAP's bare minimum recommendation of two to forward face, and are narrow for when you have two in the back are the Sunshine Kids Radians and Safety 1st Complete Air. They rear face to 40-45 pounds and forward face to 50-80 with 17.5" top slots. They have tall shells and a lot of leg depth.
If you won't turn him back rear facing, to be SAFE, again as you say, then I'd look at the Graco Nautilus or Recaro ProSport. The Evenflo Maestro would be a nice, narrow option. The one with the most leg depth is the Britax Frontier, but with a two year minimum he cannot sit in it yet (as Britax encourages rear facing to at least two, even if it means not selling seats).
It's good the Marathon fits for you forward facing. Due to the shape of our Porsche's backseat, our Wizard fit rear facing, but not forward.
If you do keep him forward, it is imperative that you tether his seat. And make sure it's installed properly. For instance, your top tether for the middle in your Rav4 is on the ceiling, not behind the seat, and LATCH is not allowed in the center. If you have him on the side you can use LATCH with a top tether down low on the seat, and the car's seat must be reclined to the seventh click. You cannot install a seat on the driver's side and in the middle, due to the seatbelt/LATCH overlap. So when you have two you'll either need to put them passenger/middle, or each outboard.
Wendy