z68 chipset would be best for you with the 2500k. z68 is more feature-complete than other sb chipsets.
differences between h61 and p67 are -
h61 allows igpu use and overclocking but no cpu overclocking.
p67 allows cpu overclocking but no igpu use or overclocking.
z68 allows cpu and gpu oc and use igpu.
h61 supplies 6 secondary pcie 2 lanes from the pch itself, p67 (and z68) supplies 8 secondary pcie lanes. the cpu itself has 16 pcie 2 lanes - usually connected to the discreet gfx card(s).
h61 supports up to 2 dimms. p67, h67 and z68 support 4.
h61 mobos are usually micro atx. p67 mobos are usually atx.
h61 mobod don't usually let users use multi gpu combinations like cfx/sli.
p67 (and z68) mobos usually lets users use x16+x4/dual x16/dual x8/x16+x8 modes.
h61 supports less usb ports. p67, h67 and z68 support more.
h61 doesn't support raid.
h61 doesn't support rst or srt, z68 supports both.
h61, h67 and p67 were affected by cougar point sata bug. z68 was affected too, but it was in production so it got new revision right away. the revised motherboards have b3 revisions.