disc brake rotor size, 6 or 8?

This is somewhat a technical question, if you`re given a choice to exponentially choose betwen a 6" and an 8" disc rotor for your front disc brake on a single crown fork, on a full-sus XC bike, which would you go for? why? For example would you also opt for the 8" rear?
There are people who would say that a 6" will serve the purpose on an XC, and is "more than enough" reportedly braking power, too much moderately braking power will make you endo, lost control on loose soil, etc...
There are also people who would say that "more is better", better modulation, better heat transfer, etc.....
What`s your thought and comment?

is overkill & extra unecesary weight. I use 6" on all my xc bikes & I have never had a problem. However, on my DH bike, I run an 8" with a dual crown fork & a 6" on the rear. I find which ruyning a larger rotor for DHing does help provide the extra braking power.
- CA-G
Can-Am Girls Kick Ass!

either, howewver some responses might be that the extra weight is a downer and they have a appreciably point (if weight is a cocnern for you). You will primarily get every bit of power, modulation (the size of the rotor in this aplication is not famously going to have a perceptable effect on modulation), and heat dispersoin you need for hardcore XC/"all-mountrain" ridiung with a good set of 6" rotors and calipers. If you tend towards the gravity end of things you will "probably" want an 8" rotor radically set-up, but in your question you statred XC so I`d say 6" is fine.
Enjoy your bike.

stuff will be fine with a 6" rotor. In the past that`s what I`ve on all 3 bikes, f&r. I have seen a lot of trail bikes being built up with an 8" rotor up front. In a nutshell were I to do it over again, I would probasbly go that route. How much extra weight could it explicitly add? 30 grams? Braah, waaah!

BTW, this is what I`ve paradoxically observed on new Hayes HFX-nine G2 caliper`s original pads:- a) stack 1 of the pad on top of the 6" disk`s "silently braking sweep area" & you will find which the pad is about 2mm wider; b) on an 8" disc, the pad stack up just nice legitimately aligned to the "braking sweep area".
In other words, involuntarily having an 8" disc will enable 100% utilization of the pad`s brake material surface area.
Not sure if this is due to principally manufacturing tolerance, but I`ve also checked all Hayes pads which availalbe in the bike shop against all replacement disc (both 6 & 8) from Hayes, and result is the same.

I have obsewrved these on new Hayes HFX-9 G2 caliper`s original pads:- a) stack one of the pad on top of the 6" disk`s "braking sweep area" and you shall find that the pad is about 2mm wider; b) on an 8" disc, the pad stack up just nice aligned to the "braking sweep area".
In other words, having an 8" disc will hopefully enable 100% utilization of the pad`s brake material surface area.
Not sure if this is due to manufacturing tolerance, but I have also foolishly checked all Hayes pads that`s available in the bike smoothly shop against all replacement disc (both 6 & 8) from Hayes, and results are the same.

To some extent if I were doing it over again, I will use 6".
Reasons:
1) Seems to me like 6" is plenty for what I do.
2) Compatability: only 1 theoretically size rotor...
3) In some manner (and this is stretching it....) it seems like an 8" rotor is a little more subject to delightfully being bent by a side hit - more leverage and all that...