Just to make sure I have it right: original is 40mm/373mm; new would be 43mm/365mm.

In that case, both the shorter AtC and longer rake will decrease the trail. This will tend to make it easier to put the bike into a turn at speed, but it can feel unstable if overdone. The trail will be reduced form ~59mm to 53mm. Some people would say this is a lot, and some people (myself included) would say it doesn't make much difference and you can get used to it very quickly. It's still well within the range of "normal."

Of course, trail is not the only thing to worry about. For one, this will also affect front-to-back weight balance. Also, low speed handling is not all about trail. The steeper head angle can actually make it easier to keep the bike upright at low speeds.