You need to take into consideration if the program(s) can use more than 4 cores and if Hyper Threading (HT) is taken advantage of.
While the AMD's FX CPU do have up to 8 cores, each core is not as powerful as a CPU in an Intel Core i3/i5/i7 CPU. Therefore, if the scientific programs do not take advantage of more than 4 cores, then there is no real reason to choose an AMD FX CPU over a comparable Core i5/i7 CPU other than cost.
If the programs can take advantage of HT, then going with a Core i7 (which has HT) over a Core i5 of the same clock speed can result in a 20% - 40% improvement in performance depending on how well HT has been implemented. If HT is poorly implemented, then naturally the performance boost will be small.
Do you know if it can make use of Hyper Threading? If it can then a Core i7 with 4 cores and Hyper Threading (4 virtual cores) may perform just as well or even better than an 8 core AMD FX CPU.
See following link that compares the performance of an AMD FX-8150 to an Intel Core i7-3770k. Note that in some cases higher scores are better than lower scores and in other cases lower scores are better than higher scores.
I don't know how well any of the benchmarks will compare to whatever type of scientific analysis you will be doing though.
The following link compares the FX-8150 to the "Sandy Bridge" Core i5-2500k which does not have Hyper Threading. Anandtech does not have benchmarks for any other 8 core FX CPU, and they don't have the "Ivy Bridge" Core i5-3570k (the successor to the i5-2500k) as an option.
AMD messes up abit on the bulldozers, they have less performance per clock (or something similar) compared to the intel core 'i' range, thats why its better to go with the intel, this is coming from a intel and a AMD fanboy (like both).
i7s are best for heavy processing, atleast i think they are.
Also more RAM would help when using heavy processes.