There would not be.  Was this for SLI or just getting more GPUs for more monitors?
 
Each slot is going to have their respective speeds with a single card which you can reference at http://www.evga.com/support/manuals/files/visual/152-HW-E878_Visual_Guide.pdf
 
but you'll see the speeds changed based on the amount of PCIe devices installed.  
Z87 Classified: 1x16, 2x16, 3x8 or 4x8
 
If you're having specific issues, let us know exactly what's going on.

just got the m/b to use for folding and if i put a 2nd card in it worked once for about a minute and then nothing from slots 2 3 4 and 5 but slot 1 works fine if only 1 card in used.even put a old gts 250 in slot 1 works fine but as soon as i put any other card in one of the other slots in hangs with the led number 15  Pre-memory North Bridge initialization started

have now tried different cords and the other monitor m/b works with 1 card any slot but add a 2nd and it will hang on code 15 and after about 3 minutes goes to windows but just black screen does not matter which card i put to the monitor to or which 2 cards i have in the m/b

the plan is to run 2 970's and 1 760 sc for folding on this board in slots 1 3 an 5.i tried slots 2 an 4 like you did an it seen both cards for maybe 60 seconds and then went black screen so i sat there an watched it for an hour still was black so i switched to slot 1 an 4 an this m/b locked up with code 15 so i took card out of slot 4 and it runs fine with 1 card but if i add another card it is code 15 or works for 60 seconds then just black screens does not matter witch card i put the monitor to worst 1.99 i ever spent.

Reset your bios to stock, with the "Optimized Default" setting, and then verify that the lanes are being changed to specific settings in the advanced menu.  Also, make sure you are fully up to date on BIOS and you have a fully updated chipset driver as well.

Postcode 15 is pre-Northbridge initialization, which can potentially mean issues with PCI-E lanes, and as it looks like you're attempting to mix three architectures, this is most likely the source of the issue. Mixing even two architectures likely wouldn't work, let alone three, and certainly isn't recommended. What you'll find is that each of these cards likely work just fine individually, but when paired (in either configuration) or with all three installed, your system will ignore two of them, not post, or experience a multitude of other issues. 
 
For reference, the 250 is a G92b, the 580 is Fermi and the 760 is Kepler.
 
(Edited to remove an unnecessary word.)

have a z77 ftw and a z87 ftw running mixed 700 an 900 series cards no problem so i fail to see why a z87 classy won't do it.

If you want big upgrade you can wait little more for Z170, motherboards will work with DDR3 and DDR4.
I know Z87 and Z97 Classified are nicest motherboards.
Performance difference will be very similar and 4790K on 4.4GHz Turbo is good as Skylake but support only DDR3.
Later only to install one GTX980 in Z97 Classy and perfect, or GTX980Ti what you like.