Your laptop is the Toshiba Satellite C600, and no, the CPU is not 460MHz, but an i5-460M, launched on Q3 2010 almost 15 years ago. Unlike newer laptops, you can probably swap out the CPU for one with similar TDP.
Reusing an old machine is good for the environment. We should encourage this.
The current CPU is 32nm on 1st generation Arrandale, 2C4T and runs at 2.5-2.8GHz with 3M of L3 cache, supporting DDR3 800-1066 RAM in dual channel. However, its old microarchitecture means newer CPUs with similar clocks have greater IPC and will perform better.
To answer your question, your laptop probably has a Geforce 310M discrete GPU, but the HM55 on laptops require the CPU to have integrated graphics for the built-in screen. This means Quad-Core 1st Gen Clarksfield CPUs such as the i7 940XM are ruled out.
This means the fastest CPU you can install in your laptop is the i7 640M.
This too is also 2C4T like the current i5 460M but runs faster at 2.8-3.46 GHz and has 4MB L3 cache. Not much of a performance increase.
You should consider first upgrading your hard disk to an SSD for responsiveness, probably a 2TB SATA drive like the Samsung 870 EVO. A larger drive may not be supported since the 32-bit controller may not recognise more than 4 billion sectors of 512K, or 2.19TB.
Then, while 2x4GB= 8GB DDR3 RAM is the maximum supported on this CPU, I have seen 1st gen Intel laptops running 2x8GB = 16GB RAM. DDR3 SODIMMs are cheap at under $1/GB on AliExpress. You can experiment with RAM sticks, but 16GB per stick are rare and thus expensive.