SamW - The HS30 still crams 16Mpix onto a 1/2.0 CMOS EXR sensor, like the HS20 - that's only 7% larger than the HS10's 1/2.3" sensor - which is "only" 10Mpix - 45% more receptor "crowding", which from the many images I've seen, doesn't help with noise or detail.
The HS10 has a BSI (back-side-illuminated) CMOS sensor - and was actually the first bridge-zoom to have such - though Canon ads in Australia claim that the SX40's BSI CMOS is "a first in long-zoom technology". It'd be true if they said "First in a 35x zoom camera", as the HS10 is 30x / 720mm equiv - the SX40 is 35x / 840mm equiv, though looking at "full zoom" SX30 / SX40 images, the "reach" doesn't seem much different.
The HS20 for some functions, and faster continuous, uses the EXR tech to "pair" the receptors on the sensor so it works as an 8Mpix camera - perhaps that's to do with the sensor crowding at 16Mpix....
The HS10 is rather better than the HS20 at high-ISO / low-light images - it does pretty clean JPEGs to ISO 800 - and 'fixable' at 1600 - though better to use RAW and de-noise at ISO 1600 up... It will do "usable" images in low light at ISO 3200 and 6400 - though they need some 'gentle persuasion' of the RAWs... However, I have straight from camera JPEGs at ISO 3200 and 6400, f/10 - f/11, in low light, heavy rain, 70-80 metres - that are 'usable' - if only as "I wuz there!" proofs.
Between the HS20/30 and SX40 - the Canon is easier to use in Auto and Program - the Fujis really need Priorities or Manual, and "being told what to do". The HS10/20/30 use the same lens assembly with twist-zoom - ideal for stills - dreadful for video - the Canons are very good with 2-speed video power zoom. The Canons also have exposure/brightness and MF in video - the Fujis have neither...
The FZ150 as you say has more manual functions than the SX40, and also does RAW, which the Canon doesn't.
Panasonic makes a Teleconverter for the FZ150 - 1.7x - and a few images with it on Flickr suggest it is quite functional, though extra glass will mean some loss of light. Price for the DMW-LT55 TC is about $160.00 in the US.
The SX40 has an internal integrated TC function - at 1.5x or 2x. This isn't the same as using "digital zoom" - it's integrated into the optical zoom by the camera's processor.
With the SX10 - TC 1.4x and 2.3x, the 2.3 is fuzzy-useless - the 1.4x is usable if you don't use the whole "virtual 28x" it offers - 24-25x on the indicator works fairly well, if you can't get the shot by going closer - okay for showing at reduced size - certainly not for printing!
So the lower option 1.5x in the SX40 might work similarly. In the SX10 the TC 1.4x is usable with video - rest or tripod needed.