You need to tell us what motherboard you have, but generally you can use the proper memory ratio and your PC2700 will work. I've seen two people say 6:5 ratio, but I don't know of any common P-4 overclockable mobo having that ratio. With the i865/i875 chipset mobos with a 800 bus CPU, you'll have three choices: 1:1, 5:4, and 3:2 ratios.
If you use the 5:4 ratio, you can overclock up to 208 FSB and still have PC2700 RAM in spec. Obviously, if your RAM overclocks well, you can go higher. If you use the 3:2 ratio, then you can overclock up to 253 FSB and still be in spec. If all this sounds way too confusing, just leave the memory ratio on auto and you'll be fine.