[MrOblongo]

Got that with this settings: (Poor)

Code:

TYPE CIRROCUMULUS
    MAT_DENSITY    0.4
    NGHBR_ABSRB    1.00
    PLANE_DISP    2
    INTERSECT    0
    TIER        2
    Z_TO_X        1.0
    N_PER_SQ    10
    DZ_Z_RATIO    0.15
    BASE_R_DISP     5
    LEVELS_MUST_BE_HERE
    LEVELS        1
    LEVEL 0
        F_UP    13.00
        F_DOWN    13.0
        F_CEN    0.0
        F_SIDE    0.0
        F_DIR    0.0
        DENSITY    5
        K_THIN    0
        K_FADE  3
        END_LEVEL
        END_GENERATOR

Good FPS
PS: Edited the NGHBR_ABSRB to 1.00, clouds looks way too dark with 0.15