Uncanny X-Men:
Onslaught Epic 4 concludes with #337.
OZT includes #346 but no more.
Seagle run begins with #351.

X-Men:
Onslaught Epic 4 concludes with #57.
OZT includes #65-70.
Kelly run begins with #70.

I would say:
UXM #338-350 (including #346 double-dip), #-1
XM #58-64, #-1
UXM Annual '96-'97
XM Annual '96-'97

Between this and OZT HC, we'd be set up for a Seagle/Kelly Omni.

How to sell this though would be another question. There's a bunch of one-shot vignettes, then over in the latter half of UXM two plots concurrently: space adventure and Gambit's trial. In XM, there's a Kingpin/Shang-Chi/Hong Kong arc. Bunches of foreshadowing and setup for OZT from various directions. "OZT Prologue" might be the only way to have any semblance of a unified title.

Samy wants to see the following collected editions:
X-MEN: CLAREMONT/JRJR OMNIBUS, X-FORCE OMNIBUS VOL. 2, 
NEW MUTANTS OMNIBUS VOLS. 1-2, GENERATION X OMNIBUS
PUNISHER (1987) #1-18 OHC,
PUNISHER WAR JOURNAL (1988) #1-24 OHC,
X-MEN: REVOLUTION OHC
X-TREME X-MEN VOLS. 1-2 OMNIBUS, WOLVERINE: HAMA/SILVESTRI OMNIBUS,
LEGION ARCHIVES VOL. 14, KNIGHTFALL OMNIBUS
LEGION OF SUPER-HEROES: EYE FOR AN EYE DELUXE HC