Ours were used in dryland broadacre applications, often under consistently high ambient temperatures (usually c.100F) predominately in seasonal 24/7 operations -direct drilling operations (for grain crops) & secondary cultivation
We found the turbo's didn't last long as the bearings fried/collapsed regularly & the best we could get out of the engines in the Cat 55/65/85 were c.6000-7000hrs before major rebuilds - we also had the 55 break a crankshaft at c.4800hrs & burn a piston prior at c.3200hrs, so maybe we had a dud.....

Comparatively the MT's ran without issues (except high track wear & a couple of collapsed track gear bearings), to c.6000-8000hrs before we exited from belted tractors, we're not hard on equipment as is evident from our older gear with high hours :
- an old Steiger 400hp with a CAT3306 still purring away at 29000hrs
- 2x White 4-150 with Cat 3208's fine @ c.12000+hrs ( a lot of people don't like the 3208's but we've always had a good run from them including in trucks & pump sets)
- 3x Acremasters 330hp mercedes V10's all fine @ 20000-36000hrs

IMO the CH55 should be ok for pulling your lettuce bed former (as they performed well in cotton on well tilled ground ) & discing, but if it's hard ground I'd be a little cautious on any heavy tine work ( like chisel ploughing ).....the rubber tracks usually wear ok in black/alluvial type soil (make certain to keep the rollers/idlers clear of soil at each day end) but experience exponential wear in granite or sandy loams....