Falconer is right about the intended allocations for karmagen. They did not change the number of karma points when the made the other changes (Attributes using the x 5 multiplier, and paying your metatype cost in karma), so the RAW number of points is the same. Which doesn't mean anything to individual campaigns, since all the points really are, is a suggested number for a typical shadowrunning campaign, which the GM is free to adjust up or down.
In my personal experience, using both character creation systems, 750 karma with the new rules tends to create slightly more powerful characters than 400 BP - or at least slightly more well-rounded ones, since you typically wind up with a few extra points to play with. This is for me, creating builds that tend to be optimized but not lopsided. For someone wanting to play, say, a troll with high natural Body and Strength scores, or one of the more exotic options from Runner's Companion, karmagen won't be as friendly. On the other hand, someone playing a generalist will wind up with far more abilities than they would under 400 BP, because the lower Attributes and skills are cheaper. Likewise, someone playing a free spirit will do much better in karmagen. Paying 250 karma leaves 500 karma for everything else, which works out a lot better than paying 250 BP and only having 150 BP for everything else.
750 karma under the old costs, or 1,000 Karma under the new costs, both give the player a lot more resources than 400 BP in character creation. This may or may not result in more powerful characters - I found that under the old karmagen, I min-maxed a lot less, and was able to explore quirky concepts that would not have been practical with less points. And min-maxed characters may not always be more powerful, either. Rather, they will be able to be specialists and have all of the other skills they need, rather than having to choose between being a specialist or a generalist. So a mix of the two won't necessarily lead to imbalance, but honestly, I would find a choice between 400 BP and 1,000 karma a no-brainer. Even if I had no intentions of min-maxing, I would pick karmagen to get more contacts and tertiary skills to round out my character.