I feel very qualified to answer!
Had the exact 8 m² Boxer model with my first foil setup.
Fell in love with foiling the waves (did strapless waveriding with kite for 10 years before touching the foil).
Then completely switched to the Peaks (4 / 5 / 8 m²). Loved them so much! Sooo much! The drift and ease of use (OK, don´t drop the into the waves
).
Then tried the UFOs. Never went back to the Peaks. Overall, the Ufo is the much better (wave) foil kite for me.
To answer your question:
Yes, the 7 m² UFO (V2) will substitute the 8 m² Boxer easily. Don´t buy the V1 or V1.1.
The 7 m² Ufo is 1,500 % more fun than the 8 m² Boxer. At least.
Yes, the Peaks drift slightly better than the Ufos. But the Ufos drift really really well as well.
And yes, the Peaks still fly in less wind.
However, the Ufo bring you up to flight in less wind than the Peaks due to their unique power characteristic. They have loads of pull when moved fast, and (actually!) total depower once up and flying. The Peak is absolutely gutless when water starting (looping doesn´t help), it needs quite a lot of wind (relatively to the wind speed required once up and flying). When the wind is not sufficient to keep the Ufo flying, I don´t have fun any more anyway. If it falls and you cannot relaunch it, then at least you have an inflated swimming aid. The Peak is a catastrophy when it falls into the water (waves!). Believe me.
The Ufos drift a bit less excellent than the Peaks, but for me this is not relevant because we have 100 % wind swell here. When the waves get bigger, the wind gets stronger too. And from 5 m² downwards the Ufo´s drift is no limiting factor at all, as the wind is fast enough anyway to make the kite drift well.