i don't envy your position as i sat in it 2 yrs ago haggling over the very same.
keep the following in mind when making your decisions:
1. Cali is very tough to break into as a DO. Most programs you will find will recommend that you take the USMLE for entry. However, entry is not impossible without it.
2. Many MD programs have no idea how to interpret the COMLEX--i can't tell you how many questions i have gotten about it and i don't have the answer either.
3. However, an MD program which REQUIRES you to take the USMLE to get into the residency, may also discriminate against DOs to begin with and may not be a program you want to be a part of.
4. the COMLEX is very poorly written and a very draining 2 days..taking yet another board exam either before or after may cause undue stress and physical drain.
My advice: call up programs in each section of the country in which you might be interested and for a variety of specialties (your ideas will change several times throughout 3rd yr) and find out what they require...then try to get in touch with folks who have been thru the game and what the real scoop is..
best of luck