Neither.
11 units
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Not but in all seriousness, definitely wait till you get to end of yr 11/start of yr 12 to decide what to drop/extensions to pick up. You may be surprised what you end up dropping and picking up. (a la me, and like a billion other BOSers)
Honestly, I am doing 12 units because I like the security, for me EE2 is always a bit of a gamble, so I'd never have it as a "definite counter". And it's not too much workload, because I did 13 units for yr 11 and start of yr 12, it seems like a manageable subject load. Things don't always go according to plan, so I personally would at least do part of yr 12 with 12 or 11 units so when you drop, it's DEFINITELY the subject that won't count. You don't want to be eating regret pie about it later.