This driver adds full support for the OpenGL 3.0 standard and resolves many issues for Windows XP and Windows Vista. You can read the changelog over here (PDF). There's no word about performance in the changelog, so I wouldn't expect any huge gains.
This release of ATI Catalyst™ provides full OpenGL™ 3.0 extension support. The following is a list of OpenGL™ 3.0 extensions added in Catalyst 9.1:
ARB_framebuffer_object ARB_half_float_vertex ARB_texture_rg EXT_texture_array EXT_texture_integer EXT_transform_feedback NV_conditional_render WGL/GLX_create_context (for new 3.0 contexts) GLSL 1.3 ARB_color_buffer_float ARB_vertex_array_object EXT_draw_buffers2