Would anyone actually notice the difference between 74mm & 80mm trail?

I think that is a fairly large difference all being said – almost 10%

From my limited knowledge that would be a similar equivalent to about 1.5 degrees in head angle.

If you go to a 80mm trail fork the steering will quicken considerably.

Do you mean rake or trail?

I think in theory with 80mm trail the bike should feel a bit quicker steering, but might suffer in the low speed tight technical stuff, like tight hairpins/switchbacks, as the slightly longer wheel base might make the bike feel less manourverable, and if you have a slack head angle it might exaggerate the flip/flop thing (not sure what the technical term for that is).

So if your bike already has a steep head angle the 80mm offset might improve things without compromising the low speed tight technical stuff too much, especially if its a 29er. But if you’ve already got a slack head angle you might be better off with the 74mm trail.

Do you mean rake or trail?

Trail. The forks in question are 45mm or 51mm rake.

6mm of trail is just under a degree of HA worth, but it’s not quite the same as adjusting the HA. Going from a 45 to 51mm rake forks on a 29er I noticed a subtly looser feel in the steering, I wouldn’t say it was less stable, just a little more neutral, less flip-flop feel. Some like that, others don’t as they associate flop with slack and stable. You get less trail which will be said to be ‘faster steering’ etc, but a longer f-c by 6mm. It’s marginal stuff really and w/o trying both on the same bike on the same day I doubt anyone would notice, I doubt I’d pick the rake in a blind test if the bike was basically sorted in the first place.

Are they Pike 29ers? They’re available in 46mm or 51mm offset. I’m pondering which to go for myself.

Had the same dilemma myself. Got the 51mm pike 29er 140mm, as I’ve posted before the fork is so much better than the Rev it replaced it’s hard to quantify where the improvements are beyond damping and accuracy. Fox 34 29ers only come in 51mm offset which is a good indication of what to go for I think.