P4 (400 or 533) 2.4 for pc2100 ram?

I bought a P4 1.5 Willy system with a "Intel" sdram motherboard(Did not know better). I installed a new motherboard for my first time and "IT WORKED OUT ALL RIGHT"! I was so surprised it when so smoothly.
The new board is a Aopen AXB-533 with 2x256mb Crucail pc2100 of ram and yes it did make a differance and was worth it to me.

My question is Im told I should replace my P4 1.5 (478 pin Thank goodness) "Willamette" to a "Northwood" for it's 512 L2 cache vs my 256 cache I have now.
Im looking at the P4 2.4 but it comes in a 400 and 533 fsb type, the 533 is $20(Canadian) more but since I only have pc2100 ram is it worth it for me to get,and is there much differance between the two kinds of p4 2.4?

Also my motherboard says it supports pc2100 but I was told I could but pc2700 in it anyways is this true and would it be worth it? All I do with my pc right now is play Bf 1942 online.


Thanks'
Tim

I would go for the 533- wont overclock to much like that tho.
Memory has become real cheap these days

whichever's cheaper or has a better stepping

400 = suck, get 533