If you really want a U87, I would strongly urge you to save that bit longer and just get one. You'll spend all your time tracking with anything else wondering if it might simply be better with an 87. Once you've owned one, you can decide first hand how close something else gets to it and if any compromises are worth it for the savings.
If you then decide to sell the 87, provided you've looked after it, you can more or less get what you paid originally. Think of it as a rental that you are getting a great deal on.
In terms of sonics, its rare for a clone to really nail the thing its cloning entirely - you will get a flavour perhaps, but its in the details that one is a Neumann 87 and one is a clone. That doesn't make the clone bad or anything, but the areas clones struggle with are what I might describe as the 'romantic' quality of the sound. The real Neumann will evoke performances you recognise from favourite records/singers etc, thats a fun vibe to worth with.
Cheaper 87 types, such as Warms 87, will do a decent impression, but there is a reason why one is £2.5K and the other less than £1K, and its not pure marketing, but years of refinement, experience and manufacturing expertise.
I have a U87 and it sounds fantastic - even if the mic is wrong for the vocalist...what do I mean? Well, it has all the quintisential qualities we want in a microphone - air, presence, clarity, extended high and can make any voice larger than life.
In my experience - it is sometimes this exact quality that can make a vocal difficult to listen to or sit right in a mix.
At such times, a less detailed condensor, or even a dynamic microphone can be preferable, but you will notice the change in quality - and you will wonder if the 87 is still the better choice regardless of it matching the audio source.
Many people dislike the U87 - I understand why to an extent, but equally to discount it or suggest its over rated is to be taken with a big pinch of salt. The U87 is as popular as it is for a reason - it is a fine microphone and somewhat epitomises 'that commercial' sound, we love.
I find if it suffers at all, it is that it can be a bit vanilla - it has the mid forward thing, but can sometimes be unexciting. Its not like the U47 or the U67 which can draw something out of the voice, or else manage the high frequencies in such a way that it pulls focus on the performance.
Its a great 'forever' microphone if you find it suits your voice or the person(s) you record. If it is a particularly good fit, I'm afraid your doomed to compare the perfomance of all microphones to Nuemann, or at least microphones in the £3K mark for the rest of your life!
Very few microphones will make you feel quite the same way.