Help!! - In choosing Ram

Hi, I’m a little bit new to some parts of overclocking and this is one of them, I would like to know witch ram I should purchase, I already have a stick of 512meg KINGSTON DDR266 (PC2100), but I feel that it's holding me back + I wont Dual-Channel DDR, so I’m thinking of taking it out and putting either of these in,

2x 256meg CORSAIR XMS2700 DDR333
2x 256meg GEIL High Performance DDR400

Do you think it would make a difference?? And witch should I buy???

My system -
Asus P4G8X Gold - BIOS Rev-1006
P4 2.53 @ 3173 @ 167 @1.58v
CPU idle 38c load 48c
Thermaltake Volcano 7+
512meg KINGSTON DDR266 (PC2100)
Asus GeForce4 Ti200 128MB @ 293C 529M
Thermaltake G4-VGA COOLMOD
Western Digital 80 gig 7200rpm 8meg Cache
LG COMBO 48x24x48x 16x DVD
ANTEC LANBOY + 2x 8cm Blue ANTEC Case Fans
MS Win-XP Pro with SP1 & Office-XP Pro with SP2

Thanks!!!!!!!!

How high do you want to overclock it??? it's always best to get the fastest ram possible so you don't have to upgrade again in a few months,,,
Geil and Corsair are both very respectable, I think most on this board would have to say the Corsair is the best for overclocking though...

get the xms. i just got a 512 stick and overclocked my 1800+ to 1.84 (11x167) its great RAM