Not sure what CS:Go graphics is, think a translation error. Maybe g-code. Anyhow I have nearly no load doing this.
Regarding the old processor and OS, what does host report in log for OpenGL. Something lik ethis would be good:

09:59:41.693 : OpenGL version:3.3 ATI-4.7.103

09:59:41.695 : OpenGL extensions:GL_EXT_texture3D GL_ARB_ES2_compatibility GL_ARB_blend_func_extended GL_ARB_copy_buffer GL_ARB_depth_buffer_float GL_ARB_depth_clamp GL_ARB_depth_texture GL_ARB_draw_buffers GL_ARB_draw_elements_base_vertex GL_ARB_draw_instanced GL_ARB_explicit_attrib_location GL_ARB_fragment_coord_conventions GL_ARB_fragment_program GL_ARB_fragment_program_shadow GL_ARB_fragment_shader GL_ARB_framebuffer_object GL_ARB_framebuffer_sRGB GL_ARB_gpu_shader_fp64 GL_ARB_half_float_vertex GL_ARB_imaging GL_ARB_instanced_arrays GL_ARB_internalformat_query GL_ARB_map_buffer_range GL_ARB_multisample GL_ARB_multitexture GL_ARB_occlusion_query GL_ARB_occlusion_query2 GL_ARB_pixel_buffer_object GL_ARB_point_parameters GL_ARB_point_sprite GL_ARB_provoking_vertex GL_ARB_sampler_objects GL_ARB_seamless_cube_map GL_ARB_shader_bit_encoding GL_ARB_shader_objects GL_ARB_shader_texture_lod GL_ARB_shading_language_100 GL_ARB_shadow GL_ARB_sync GL_ARB_texture_buffer_object GL_ARB_texture_buffer_object_rgb32 GL_ARB_texture_compression GL_ARB_texture_compression_rgtc GL_ARB_texture_cube_map GL_ARB_texture_env_add GL_ARB_texture_env_combine GL_ARB_texture_env_dot3 GL_ARB_texture_float GL_ARB_texture_multisample GL_ARB_texture_non_power_of_two GL_ARB_texture_rectangle GL_ARB_texture_rg GL_ARB_texture_rgb10_a2ui GL_ARB_texture_swizzle GL_ARB_timer_query GL_ARB_uniform_buffer_object GL_ARB_vertex_array_bgra GL_ARB_vertex_array_object GL_ARB_vertex_buffer_object GL_ARB_vertex_program GL_ARB_vertex_shader GL_ARB_vertex_type_2_10_10_10_rev GL_ARB_viewport_array GL_ATI_texture_mirror_once GL_EXT_blend_minmax GL_EXT_draw_buffers2 GL_EXT_draw_range_elements GL_EXT_framebuffer_blit GL_EXT_framebuffer_multisample GL_EXT_framebuffer_object GL_EXT_framebuffer_sRGB GL_EXT_geometry_shader4 GL_EXT_gpu_program_parameters GL_EXT_gpu_shader4 GL_EXT_multi_draw_arrays GL_EXT_packed_depth_stencil GL_EXT_packed_float GL_EXT_packed_pixels GL_EXT_pixel_buffer_object GL_EXT_shadow_funcs GL_EXT_stencil_two_side GL_EXT_stencil_wrap GL_EXT_texture3D GL_EXT_texture_array GL_EXT_texture_buffer_object GL_EXT_texture_compression_s3tc GL_EXT_texture_edge_clamp GL_EXT_texture_env_add GL_EXT_texture_env_combine GL_EXT_texture_env_dot3 GL_EXT_texture_filter_anisotropic GL_EXT_texture_integer GL_EXT_texture_mirror_clamp GL_EXT_texture_object GL_EXT_texture_sRGB GL_EXT_texture_shared_exponent GL_EXT_transform_feedback GL_EXT_vertex_array GL_SGIS_generate_mipmap GL_NV_texture_rectangle GL_EXT_texture_swizzle GL_ARB_map_buffer_range WGL_ARB_extensions_string WGL_EXT_extensions_string WGL_ARB_pixel_format WGL_EXT_pixel_format WGL_EXT_swap_control WGL_ARB_pbuffer WGL_EXT_pbuffer WGL_ARB_create_context WGL_ARB_create_context_profile WGL_ARB_framebuffer_sRGB WGL_EXT_framebuffer_sRGB WGL_ARB_make_current_read WGL_EXT_make_current_read WGL_ARB_render_texture WGL_EXT_render_texture

09:59:41.695 : OpenGL renderer:Parallels using AMD Radeon Pro 580 OpenGL Engine (Compat)

09:59:41.695 : Using fast VBOs for rendering is possible

Most important is "Using fast VBOs for rendering is possible" - that is the fast, graphic card powered 3d solution. With older OpenGL versions viewing g-code is quite slow due to missing hardware support and can easily consume 100% cpu time then.