Well, it's sounds like BOTH of you want to do it BUT you guys are both scared of what will happen after...
Will your relationship become more strong or will it get weird and fall off?

You guys gotta talk and figure out if you are both willing to try, if either one of you IS NOT interested to find out then I would suggest staying as friends and not doing anything. If both of you talk and you both understand the risks that come tied in with making that step then by all means unload one on her for me.

The thing with just being friends with privelages is that they most often end up in friendships being lost... At thats because when theres sex involved theres no friendship in some sense. Let me explain why...
Once you start sleeping together emotions and feelings on both you and her start to changer.... Keep in mind you guys are ONLY friends, next thing you know one day she gonna see you with someother girl just talking and shes gonna ask you joikingly is that your other girl? (Notice how she would say OTHER girl insinuating she is yours) and little by little things will start to get a little rough because since you guys don't have a defining line of whats OK and what isn't you might get jealous about something she does and visa versa....
Relationships like that don't last much cause you guys will always just be in between with nothing really certain...
Thats why I tell you sit down and talk and decide wether you guys are willing to take it to the next stop or not.... If you guys are and you guys are willing to go on with whatever turns out then good luck to the both of you and always keep in mind what has held you totgether as friends for such a long time.....
If you guys ain't then BOTH of you back off BUT really back cause I'm telling you that 'Friends with benifits' almost always ends up bad....