I don't think a mobo with a Celeron would support any i5. And not all i5 are quads.
A bottleneck is a [lace where things slow down. Think of a three lane road that narrows to two lanes. Traffic moves more slowly as the road narrows. In terms of computers you can have the fastest processor available, but if you have a slow Internet connection it will cause things to slow down as it goes through that bottleneck.