More money doesn't always mean more stress. In the same organisation that may be true, but moving to a different sector may mean that things are less fast paced. I'm a PM myself working in healthcare IT and it can be pretty stressful at times. My girlfriend has just moved from being a Dev Manager in healthcare IT to one in the financial sector and is finding it really easy (Which she hates) despite having been given a huge pay rise when moving... She's now looking at getting her boss' job as quickly as possible.
I'm in a very similar position to you as I have worked for my company for 11 years. Leaving would be hard, but there are so many good opportunities out there. Who know's if you do hand your notice in, your company may try to keep you by offering a better package or another role? In a small company there is sometimes not natural route for career progression, so leaving is unfortunately the only thing you can do in order to improve your career.
Wish you all the best and with a big enough pay rise you might be able to tempt Matt to sell you the Zed back!