I use WY1968 a lot, and I can definitely say that it is much fruitier when underpitched than when overpitched. I don't make starters when brewing a bitter with it just so I can get more esters. When I use the yeast cake to brew IPA after the bitter is done, it is far less fruity.
I have found the same is true with wiessbier yeasts 3068 and 3333. Far less banana when you use a yeast cake.
Back to the original question....while WY1968/WLP002 can give pretty good fruitiness, I have had my best luck with WLP023 Burton yeast.
Also....try the old trick of "dropping"....about 14 hours after you have pitched the yeast and fermentation has started, put your spigoted fermentation bucket on a table, open the spit, and let the fermenting wort "drop" into another primary fermenter. That trick, which I read about years ago on the HBD, always seems to increase the esters a bit (as well as adding just a hint of diacetyl, which I also like.
Also, check your hops....I find that Target gives a kind of berry flavor to a bitter.