Question regarding tombstone removal and compaction

[Fredrik]

We've had a bug that caused one of our column families to grow very big 
280 GB on a 500 GB disk. We're using size tiered compaction.
Since it's "only append" data I've now issued deletes of 260 GB of 
superflous data.

1. There are som quite large SSTables (80 GB, 40 GB etc..). If I run a 
major compaction before GC grace, which is 6 hours, will the compaction 
succeed or will it fail due to the GC grace hasn't elapsed and thus 
major compaction will ignore the tombstones and then fail due to 
insufficient disk space?

2. If I wait until GC grace has elapsed, will it be possible to run a 
major compaction since there are only deletes which doesn't require 
double amount of SStable size when merging tombstones with the large 
SSTables?

Regards
/Fredrik