I currently drive an E36 M3 sedan and am considering the purchase of an E39 M5.
As I look at various ads on autotrader I noticed a few differences in interior trim.
The leather on the seats and lower backrests on some models is a sold leather panel. I have seen other cars where the same area looks to be leather strips stitched together in long seams.

Was there a specific option package that determined the leather stitching on the seats?
Does anyone know why this is? Are there benefits to either style?

Thanks for the help!

(Sorry I can't post pictures yet or I would have shown some examples.)

m5board.com might be better place to ask this, not many m5's on this board.

Ok, thank you. I will post the question there as well.

The seats with the solid leather are the sports seats, which i prefer over the luxo seats (ones with leather strips stitched together. Typically the luxo seats come with the wood trim as well as the leather dashboard. I'm not 100% sure about the other differences, but thats all I really gathered during my m5 search.

Full leather (ones with stripes) and extended leather packages

Read this thread:

http://www.m5board.com/vbulletin/showthread.php?t=110237

In summary then...

Sport package - color option inserts for seats and trim
Luxury - pleated leather with matching trim
Extended leather interior = leather dash.

Thank you for all the responses. I believe that answers my questions.

Thanks for the help!

sport package (which also had a two tone option) vs. luxury package (monotone, with vertical stiching) full leather was optional as well, which covered the dash in leather as well.

Is there any benefit to either style (comfort or durability) or is it simply cosmetic preference?

I have heard---key word---that the leather treatment used on the dash of 2000-model cars with the extended leather package renders it more susceptible to UV damage than 2001+ models. There was some debate whether BMW actually swtiched to vinyl/leatherette for the dash of the later cars, but apparently BMW offically responded that no, it was all real leather throughout the entire production run. M5board has more on that subject...

Is there any benefit to either style (comfort or durability) or is it simply cosmetic preference?

The luxury interior leather is softer and smoother. The sport has a texture to it to give more grip. Both should hold up well if you care for them.