If it only occured in the last few weeks, check if your system drive is nearly full. Try to keep approx. 20 GB free, also check if you can increase the RAM, that may be cheaper than a new machine.
I'm not sure if you're just complaining or if you're looking for some advice. You're not going to change a basic tenet of computer software and hardware by buying a PC. You will merely be buying a PC that has more power than your current Mac. It's like buying a new pair of shoes and complaining that the old pair, which you've had for 6 years, are just not comfortable and you'll never buy a pair of those again. Most likely, they were great 6 years ago -- otherwise you would not have worn them for 6 years.
As for your new Canon, I assume your old camera did not produce 21GB files. Let's say you came from 10 GB RAW files. Any software and hardware will take more time (about 100% more time) to process 20 GB than to process 10 GB. There's no way around it.
Do you have any specific questions that someone might be able to help you with?
Seems to be a complaint.
Back on Novemeber 15th in this post https://discussions.apple.com/message/16739426#16739426 he already declared he was getting rid of his MBP and buying a PC.
John Tweddell wrote:
have decided its time to vote with my feet .... have decided to now purchase a PC to replace my core duo MBP.
If your camera creates 21GB raw files you're doing something extremely wrong. I think you mean megabytes...
Now that I've got that minor detail out of the road, for any laptop to last 6 years is impressive, so I'm not sure why you're complaining that it's finally met its match.
As for your question, the inability of a computer to efficiently and effectively run the software it needs to is when it stops being a great computer.
As for what you end up buying to replace it, that's your decision. If you believe you can get 6 years from a PC, go for it.
Take your ponits - I will go for a Apple when I can afford it, Issue is my pension and lack of spending power .. Its a shame it seems to have slowed down so much. I am sure its part camera foile size - but issue is a lot worse in last few weeks (since the update). Dont mean to moan, but it is really slow.
Assume other than running only one app, there is not much I can do.