You do not need to upgrade your CPU, there are DDR3 LGA775 motherboards out there (http://www.newegg.ca/Product/Product...82E16813131395).
But, the question you really should be focusing on is, "Should I upgrade my CPU". DDR3 benefits do not really warrant an 'upgrade', but if you were to upgrade your CPU you would probably be better off getting a DDR3 motherboard then.
All in all, you do not really "need" to upgrade. Your CPU should be more then enough for SLI and games (with a nice overclock), and as far as CAD goes, your CPU should be adequate for it. IMO, you should wait till AMD's 6 core desktop CPU comes out next year, then compare Intel/AMD and upgrade options.
But, the question you really should be focusing on is, "Should I upgrade my CPU". DDR3 benefits do not really warrant an 'upgrade', but if you were to upgrade your CPU you would probably be better off getting a DDR3 motherboard then.
All in all, you do not really "need" to upgrade. Your CPU should be more then enough for SLI and games (with a nice overclock), and as far as CAD goes, your CPU should be adequate for it. IMO, you should wait till AMD's 6 core desktop CPU comes out next year, then compare Intel/AMD and upgrade options.