Far be it from me to advise anyone when to ride or not. But if you DO want to ride in the cold, I'm someone who's figured out how to ride in 35 to 40F for 12 miles at freeway speeds. Here's what has worked for me:
1) A windshield. A proper screen will be equal to a whole other layer of clothing. I've been pleased with this one and I'm picky:
http://www.twistedthrottle.com/mra-v-flow-x-creen-sport-screen-style-vfxs-windshield-for-naked-sport-bikes-cruisers-enduro-and-dual-sport-motorcycles2) Insulation. If you don't want to invest in or mess with heated clothing, I've found the phase-change gear from BMW to be an excellent alternative. Light and effective.
Jacket liner:
http://www.amazon.com/BMW-Phase-Change-Jacket/dp/B006LM02EUUnder pants:
http://www.amazon.com/BMW-Genuine-Motorcycle-functional-underpants/dp/B009I48N8A/ref=sr_1_1?ie=UTF8&qid=1386740490&sr=8-1&keywords=phase+change+pants3) Heated gear. There's a huge leap between keeping your own heat to yourself with insulation and adding heat into your body from outside itself. I deem heated clothing up there with velcro as something that has changed our world! It has certainly changed my entire view about riding in the cold.
If you're worried about affecting your range (100 watts is a tiny percentage of what your bike uses), you can use external batteries. I have a Jett vest from Australia with a rechargeable battery that would be very good at 45F by keeping the blood going through your kidneys warmed. Be sure to wear a heavily insulated outer jacket over it.
http://www.jett.us.com/I have also used Gerbings gloves with rechargeable 12V batteries that fit into pockets on the back of the cuffs.
http://gerbing.com/collection/g3-glove.htmlMost days now I wear the Jett vest and plug some First Gear heated gloves into a jack tie-wrapped onto the handlebars and hooked up to the Empulse's 12V tap through a fuse block.
On super cold days, I have a Gerbings jacket liner into which I can also plug the gloves. This combo uses about 100W of juice and has never blown the bike's 12V fuse.
I travel about 30 to 40 miles a day, including 25 miles of freeway, 5 days a week on my job and don't have a car. Thankfully it almost never freezes in San Francisco. Unlike Gavin, I'm not an ice rider.
I find the heated gear really good for coming home after dark, when I'm hungry and my blood sugar is dropping and I'm just plain cold inside out. I'll get on the bike just to warm up! No amount of insulation seems to provide that kind of thermal resuscitation.
In San Diego, I'd think for the few times it gets to 45F, a heated vest and a well insulated riding jacket, some thermal underwear under windproof pants, boots with wool socks thick winter gloves would do you just fine. And is there any reason you HAVE to travel at 80 mph? It's way warmer, even with a windshield, at 65!
Finally (at last!), I consider heated gear a genuine safety benefit. I've been so cold and wet on bikes that I could barely operate the brake and clutch levers, barely concentrate on what was going on around me, and shivering so hard, I'm not sure my muscles could react fluently in an emergency maneuver. Not good. I've NEVER been in that state since springing for heated gear. YMMV.