The plus and the ultra both have relatively fast tips with the real difference being lower down towards the first joint and below
This is where the plus starts to have more resistance to bending and I’d say this additional resistance feels to me roughly around 20% more.
The plus is a far more useful rod imo because it will do everything apart from the most extreme.
The tip is fast enough and soft enough to comfortably bring a bag full of roach to the net yet the middle and lower sections are beefy enough to bring a barbel out of the main flow with patience and space.
If there is any weight difference between them it’s single figure digits and not even worth considering.
I’d only chose an ultra over a plus if I was choosing a dedicated rod for fish up to 3/4lb maximum to simply maximize the rod and get the best out of it. While both are happy bringing 12oz fish to a net, the ultra is doing it in it’s sweet spot and more of a pleasure, the plus will want another pound on it to feel equally as sweet.
If acolyte were to bring out an SU plus model for lines up to 8lb in 13/14/15 and a 17 plus model, i don’t think there would be a logical reason to use any other brand of rod for float fishing. No finer way to spend £200-250 in my opinion