Hi, the 2140 is the new version of the 2120. If you have had the 2120 recommended the 2140 should also be fine. Go to a specialist shop and get fitted out.
Is the heel in the Nimbus much softer than the 2140? If so, the relative instability combined with additional heel softness in the Nimbus could cause achilles problems. Were you having problems in the 2140s? If not, I'd definitely get your gait re-checked. From 2140 to Nimbus is a fair old jump down in stability.
Just wondering if anyone knows the difference between the two models of shoe. I have had the GT 2140 and loved them but have seen a special offer on the 2150 but cannot find any comparisons between the two. Thanks