I\'m looking for a fast BigFloat unit, which can deal with addition, subtraction, multiplication and division (log would be fine but isn\'t necessary) and which has a precis
To summarize the comments to the OP's question.
A C library is probably the best solution for a big floating point library.
GMP claims to be the fastest free library, optimized with assembly and established since 1991.
Use this Delphi wrapper for the GMP library.
For even faster speed with reasonable cost/effort a CUDA/GPU solution would do the job. There are work going on, but I could not find a finalized solution.
Software floating point is inherently 1 or 2 orders of magnitude slower than hardware floating point. Couple this with the fact that you are looking for much greater precision and you probably have another order of magnitude.
Your expectations are probably unrealistic.