The acceleration #'s for the new 35i is about equal to your V-8, with much improved mpg figures due to the 8-spd tranny, while the 35D has gobs of tq (425tq/265hp), but is a little slower and louder than the gas counterparts. Test drive both to figure out which one you like more.

As for your current X, has it been relatively trouble-free? That would be a major deciding factor as these cars like to pop up w/electrical gremlins every so often. Are there any visual blemishes, tire tread depth? Both of these could cost you upon lease return.

I would go into this w/an open mind, and a set budget for both new and used. Don't tip your hand about your ultimate intention until the #'s are to your liking.

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11' X5 35i Sport Activity - AW/Blk/Alum
06' Subaru Legacy GT - GONE
05' BMW X3 3.0 - GONE
01' Honda Prelude, modded - GONE