Putting Trent 500s on an A343 would be rather exciting! Over 100 tonnes of thrust on a 260 tonne airliner would solve any climb problems, certainly. Not sure the accountants would like it...
The A346 climbs a great deal better than the A343, even though it weighs 100 tonnes more. I'd say it climbs better than my previous aircraft - the late-model B742 with D4 RR's on.