What you're trying to do would most likely work with certain desktop boards for such an upgrade. However, most of the time with notebooks, especially ASUS models, their SKUs are usually the highest you can do within the same CPU architecture, even despite having done the microcode update yourself.
Now clearing the CMOS with ASUS notebooks does not act the same way as it does with desktops. The most that will happen is the date/time will be reset, no BIOS settings will actually default. In this regard with ASUS notebooks, settings changed in the BIOS are not saved into SRAM (why CMOS reset doesn't work) but written to a module in EEPROM (NVRAM). This is also why a lot of ASUS notebooks are in RMA after some settings already saved are being corrupted with being overwritten again and the boot and recovery blocks are then no longer accessible, rendering the notebook with no keyboard lights or even recognize any key commands (requiring hardware programmer to resolve). ASUS has limited a lot of features and user control within the BIOS and their MB PCB design/Chipset (supporting) that allows for anything outside their models/SKUs.
It is not the power supply unable to provide the TDP of the CPU, but rather, it's the aforementioned above unfortunately.
Some people have gone from 45W 3610/30QM CPUs in a G75 to a 3940XM which is TDP 55W without issues except for Turbo Boost clocks fluctuating a lot (varies with each system if not at all in some). Even if Sandy Bridge and Ivy Bridge are backwards compatible, it's unlikely to be successful upgrade with ASUS notebooks (specifically) just by a drop-in upgrade.
This kind of makes sense now, but the iGPU has been disabled using certain modules/callbacks in most of ASUS G-series notebooks. So the fact your system stays powered up with a black screen and doesn't shut down right away tells me you need the correct PEI/DXE modules from a G75 system BIOS perhaps (with experimentation) since it's most likely initiating the internal graphics of your 3740QM where the BIOS has limited this control for Sandy Bridge CPUs, therefore conflicts regarding which has first VBIOS boot priority is undetermined.
Hopefully this helps answer some of your questions.