I also cannot see that the 116i would give any real advantage over the 118d and the cost diference when the depeciation is considered would be a bitter pill to swallow.
Also consider, that all the new 1er engines are direct injection for both diesel and petrol so they appear to have similar carateristics now. The 116i you drove may have had the Sport auto in it, so that could also vary the results. The Sport auto when in 'Sport' selects 1st gear to launch and allows for later changes, giving the appearance of better performance. I would keep your 118d and have it chip tuned- happy days ahead-