The strap is the start-point for the system.
E4x00's strap at 200MHz True/800MHz System Bus
E6x00's strap at 266MHz True/1066MHz System Bus
The P965 Northbridge is designed to run at 266MHz/1066MHz or 1:1 with Core2Duo's.
OK - so what? Well, those numbers have to interact with the Northbridge and Memory Controller and the Northbridge also runs multipliers to keep it at or near a constant speed (the strap). When the Northbridge runs out of headroom it slows down to the next multiplier down which reduces memory bandwidth and slows up the system until you add enough extra FSB to overcome the extra latency the motherboard is inducing. I think the LDT thing on AMD's is a similar issue ie. to clock higher you have to reduce the LDT otherwise you overclock the abilityof the Memory/Northbridge/CPU to talk to each other.
So how does this work in reality?
E4300 - Strap is 200, Northbridge on a P965 wants to run at 266MHz so it runs a slower divider until that one runs out of headroom at about 333MHz and it changes to the 266MHz strap the E6300's were using all along.
E6300 - Strap is 266, and on most 965 boards the Northbridge divider runs out at about 425MHz and it changes to the next one up (333MHz) and it actually runs slower because it's strangling the memory bandwidth until it comes back at about 475MHz, which is why everyone says avoid the 425-475MHz strap black hole on the P965 boards, which is why Easyrider is correct when he keeps banging on about E6400's. They sit in the strap "sweet spot" at all times.
The thing is that the E4300 is in that black hole when it first starts up, and it doesn't get out of it until it's running at 266MHz and then it's back into the black hole after 333MHz when it also changes strap again. You're not avoiding the strap change, you're just moving it downwards. You can confirm this by running SuperPi at either side of the strap change.
The only way to avoid this is to run a board that is designed to run from 200MHz/800MHz like the 975X boards or the earlier 865 boards. They actually allow you to pick the bootstrap you want to use so give yourself CPU and/or RAM bandwidth overhead.
An E4300 in an ASRock 775i65 with fast DDR RAM will overclock pretty well, as will an E4300 in a Bad Axe or a DFI 975X board.
