I actually bought my Marlin for the express purpose of converting to 358 but since playing with the 35 Rem I didnt think it was neccessary. The only reason for me to do so is brass availability. Where I am the 35 Rem never caught on, so ammo and brass are rare to find here.
The SAAMI spec for the 35 Rem is around 33K and this was designed for safe functioning in the old Rem autoloader (Model 8?). In a Marlin you can increase the pressure to what is considered safe for a 30/30, ie around 42K.
With the right powder this will narrow the gap on the 358 and still be safe to use in a Marlin. My handloads for a 200gr bullet develop around 2250 fps and you could probably safely achieve higher velocities. Buffalo Bore have +P loads pushing 220gr bullets at 2200 fps and these are safe for use in a Marlin.I have developed cast bullet loads that push a 250gr pill at around 2000 fps.
