Clethodim and Butyrac200 are about the same rates for clover and I would definitely use crop oil. For application rates the CLETHODIM 2E label reads; When using hand sprayers or high volume sprayers utilizing hand guns, mix 1/4% to 1/2% (0.33 oz. to 0.65 oz. per gallon) CLETHODIM 2E and treat to wet vegetation, while not allowing runoff of spray solution. For uses requiring crop oil concentrate, include crop oil concentrate at 1% (1.3 oz. per gallon) by volume. For uses requiring non-ionic surfactant, include non-ionic surfactant at 1/4% (0.33 oz. per gallon) by volume. I also use approx. these rates for the Butyrac200.
As far as tank mixing, I do that all the time; CLETHODIM 2E label also reads; CLETHODIM 2E TANK MIXES WITH BROADLEAF HERBICIDES (REFER TO THE USE DIRECTIONS TABLES IN THIS LABEL FOR SPECIFIC GRASSES AND GROWTH STAGES) (1)If grass regrowth occurs or an additional flush of new grass emerges, make a second application of CLETHODIM 2E alone (without a tank mix herbicide), according to the appropriate size and rate directions. (2)Broadleaf weed control may be reduced when grass populations are tall or dense enough to intercept the spray pattern and prevent them from receiving complete coverage. Tank mixing is not recommended in these situations. (3)Always use a crop oil concentrate at the listed rate (but not less than 1pt./A) in the finished spray volume. (4)CLETHODIM 2E plus 2,4-DB may increase the severity of crop injury when tank mixed.
Butyrac200 is also labeled for tank mixing, I have mixed these two with no adverse effects.
I'm late to this discussion, but the next time you need to buy herbicide for clover check out "Thunder" (Keystone Pest Solutions $319 per gallon, 1 gallon treats 32 acres, $10 per acre), this stuff does better on broadleaf weeds for me than any other product, and although it looks expensive, the cost per acre isn't that much. For some more info on spraying clover read my post #37 in my thread Keystone Krops