The SX40 HS would be a fine choice, you'll be able to crank up your ISO higher and get cleaner results than with your SD780, but if you really want the best performance in low light and the littlest motion blur, a DSLR would be the best choice. By opting for a DSLR, you'll be able to step up your ISO much higher than with a compact, making it a much better choice for shooting in low light. You'll also be able to get some fast prime lenses for even better low light performance, something that a compact can't offer. Shooting movies is also better, even the entry level models such as the Nikon D3100 can shoot full 1080P video at 24FPS. The only real advantage a new compact camera like the SX40 HS would offer would be a better zoom range and somewhat better low light performance.
If you decide to opt for the compact camera, the SX40 HS is a fine choice, but for your priorities I think that you really should consider a DSLR. You may want to consider a Canon 1100D with its kit lens and perhaps a Canon 35mm f/2, or a Nikon D3100 with its kit lens and a 35mm f/1.8. That will give you lots of versatility, the only thing that the Powershot could offer that the DSLR couldn't is the telephoto zoom range, but for your needs that doesn't seem like a huge priority. If it is, consider an 18-200mm DSLR lens.
Hope that I helped!
Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories
"There are no rules for good photographs, there are only good photographs."
- Ansel Adams