TO:luvspoodles.
Monterey water is as cold as it gets in California. During summertime, Monterey also has highly variable vis due to planktonic bloom secondary to increased sun light.
The southern Channel Islands (Santa Barbara, Santa Catalina, San Clemente) usually have warmer 60-68 degree water, fairly good clarity (40-60ft) in the summertime. Lead is a function of skill level and thermal protection fit. Not knowing your musculo-skeletal build, but assuming average, for a woman, 16-18 lbs of lead using a comfortable 7/6/5mm attached hooded or detached 12mm Otter Bay hood can be expected. If you are average, yet needing more lead than this, then work on optimal weighting, neutral buoyancy and RELAXING. Not being able to breath(SOB) is usually related to too tight a wetsuit (particularly in the chest - 2 piece Farmer-John style suits are notorious for this) and SOB is also related to a poorly designed BC bladder/strap system. If you rented your stuff, then dollars to donuts, equipment changes hopefully will solve your SOB. Live-aboards to the southern channels may possibly be worth exploring, given your situation.
Consider double hooding or purchasing a pre or custom made 12mm hood from Otter Bay Wetsuits & Drysuits in Monterey at 207 Hoffman Ave., Monterey (near Hoffman & Foam) toll free 888 220-1453. Comfort is everything in cold water California diving.
As I recall when I've done the Marine World thing in Vallejo, CA, the shark exhibit had a big map that lit up for each species of shark and Stumpy, the Great White Shark, was in the Carribean, western US coast, Hawaii, ... just about everywhere. Satellite tracking experiments show that GW sharks frequent seal haul out territory along California, too often hit surfers, and breed along the coldest parts of California (Santa Cruz north/ northern California), then in late fall/winter swim 3500miles to be in Hawaii. I have hundreds of dives and have never seen Stumpy. These apical predators have more than the 5 senses you and I have; in addition, they have chemoreceptor, pressure receptor, and electrical receptor sensory abilities - from miles away! Sorry, but IMHO, if you are lucky enough to see Stumpy before he strikes, then he is currently ruling you out as a course on today's dinner menu. Since SCUBA divers very rarely SEE Stumpy, then I conclude he has, long before humans ever could possibly see him, he has decided we're not worth eating. Even if GWS aren't in a particular local, there definitely is a look-alike to fit his same niche. He might have tiger stripes, he might have huge dorsal fins, he might have more frightening teeth - but they will be every much as big and potentially deadly. I have never seen Stumpy; I have seen some of his slightly smaller brethren because I've gone to swim with them. Low California vis and an active imagination can cause you to be very anxious and not RELAXED in our California ocean. Unfortunately the probability is either zero or 100% that you'll experience an encounter. Most avid California divers anecdotally believe that not carrying bloody speared fish, not spending too much surface time, not swimming with the seals, and most importantly not wearing any metal while submerged will reduce the risk.
Tell me, before you became a diver, what color was the ocean?
Here's another compelling question, how would you feel about something much bigger than you (but not near the size of a big GWS), if something much bigger than you swam up from behind and was within feet or even nipping at your fins, how would you feel?