I tried out combo number 1 today in a pair of games. I got the 4+ invulnerable save, guide, and prescience in the first game and prescience, fortune, and ignore cover in the second. The ability to re-roll all hits and re-roll all saves made for an incredible unit. They kept everything out of a 24" bubble and effectively controlled an entire quarter of the board sitting in ruins.
A friend of mine brought up an interesting combination. 4 grotesques joined with Karandas joined to a unit of 4 grotesques (or larger) with a liquifier gun. They can outflank or infiltrate and flame or assault (if you go second). Fearless, FNP, stealth, and a high toughness. A difficult unit to shoot off the table and a will threaten most any unit in an assault.