Yeah, it does matter about the core since they can use a completly differnt archietecture.
And I'm afraid your motherboard won't work with something more than a 3.2 if it says it
It might be because it starts using a different pin amount which isn't compatable. Though firstname.lastname@example.org is a excellent overclock anyway!
Plus it might be the reason why you can't overclock more than 3.2 since your motherboard only supports them speeds.
I'm afraid if you wanted to overclock, you'd have to buy a new motherboard and new CPU
I hope this clears things up