This isn't true. The difference is that the MK10+ uses a rounded piston instead of a knife edge, and the seat is the same as the current MK25 seat. The idea behind the MK10+ was primarily increased flow rate, as the rounded piston edge allowed for more aerodynamic efficiency of getting air into the ambient chamber. An additional (claimed, anyhow) benefit was increased seat life due to the lack of a knife edge.
Unfortunately, in terms of IP stability, it didn't always work out; the piston was known to have some creep issues, like the middle generation MK20. If they ever started making an updated MK10+ piston that works like the MK25 composite piston, I'd gladly convert my MK10s.
In terms of pressure usage and cold water performance they would be identical, with the exception that the MK10+ with it's higher flow rate could (I guess) be theoretically more prone to freezing.