Orc Archers are not really that hard to kill. It also depends on the features of the server you're in right now. For instance, if the server has healers and such, you can simply use an archer and go back and forth the map (whether there's a warper or warp).
Another thing, it also depends on the gameplay you prefer, and this varies from one person to another. If you depend on healer or warper/warp portals - then restocking your sp via those available nps would work. However, some people may not like map-hopping gameplay. Flee-type DPS classes (such as hunter/sniper, sin/sinx, etc.) are always good to have if you wish to stay in one single map for a long while.
You said it's a lowrate Pre-Renewal. (but if you prefer a midrate, check CGRO) If i were to play in that server, I'd go for assassin or sinx, alt a soul linker for assassin spirit, use jamadhar bought from NPC, and use a sage to endow myself with fire. I'm pretty sure that's enough build to 1hit an Orc Archer. Use Teleport INSTANTLY right every skill (assuming you can 1hit the mob). That should give you a quick way to farm OAB.
